French Onion Broccoli Cheese Casserole: The Ultimate Comfort Food Mashup

There are few dishes that instantly conjure up the feeling of warmth, luxury, and pure indulgence quite like French Onion Soup. That deeply caramelized sweetness of onions simmered in beef broth, covered in a thick blanket of nutty, melted Gruyère cheese—it’s culinary perfection. Now, imagine taking those iconic flavors and merging them with the timeless, creamy tradition of a classic broccoli cheese casserole. The result? The show-stopping French Onion Broccoli Cheese Casserole. This is not your grandma’s side dish; this is a gourmet comfort food hybrid that elevates the humble broccoli bake to a main-course-worthy masterpiece.

This recipe for French Onion Broccoli Cheese Casserole transforms simple ingredients into something extraordinary. We start with the essential step: slow-cooking yellow onions until they release their natural sugars and deepen into a rich, savory jam. This forms the soulful core of the dish. That intense flavor is then folded into a velvety smooth, homemade Béchamel-based cheese sauce, fortified with sharp white cheddar and, of course, the requisite, luxurious Gruyère. Finally, fresh, bright green broccoli florets are smothered in this decadent sauce and topped with crispy French fried onions for the ultimate textural contrast. Whether you are searching for the perfect holiday side dish or an elevated weeknight dinner, this French Onion Broccoli Cheese Casserole delivers layers of savory flavor that will have everyone reaching for seconds. Prepare to be amazed by this rich, cheesy, and deeply satisfying culinary adventure.

Why You’ll Love This French Onion Broccoli Cheese Casserole Recipe

This French Onion Broccoli Cheese Casserole isn’t just another addition to your recipe repertoire; it’s a guaranteed showstopper that brings sophistication and intense flavor to any table. If you cherish both the savory depth of French Onion Soup and the creamy comfort of a classic casserole, this fusion recipe is tailor-made for you.

A Symphony of Umami and Sweetness

What truly sets this French Onion Broccoli Cheese Casserole apart is the complexity of its flavor profile. Unlike many casseroles that rely solely on processed soups or simple cheddar, this recipe builds its foundation on carefully caramelized onions. The 15 to 20 minutes spent patiently browning those yellow onions is the most crucial step. This process creates deep, rich, umami notes, balanced by a natural sweetness. Deglazing the pan with beef broth and Worcestershire sauce adds a savory kick, mimicking the deep, meaty base of the traditional soup. When these glorious onions are combined with the sharp, nutty Gruyère and cheddar sauce, the resulting flavor is exponentially richer than standard broccoli bakes.

Texture That Triumphs

A good casserole must have textural contrast, and this one excels. The base is wonderfully smooth and creamy, thanks to the homemade roux-based sauce that envelops the tender broccoli florets. Layered on top is the magic of two different finishes: first, the remaining ½ cup of nutty Gruyère cheese melts beautifully, creating a gooey, irresistible crust. Second, the French Fried Onions provide a necessary, dramatic crunch. Baking them in two stages—a partial bake followed by a final, high-heat blast—ensures the topping stays golden brown and irresistibly crisp, preventing the dreaded soggy crust common in many casseroles. The combination of soft broccoli, creamy sauce, and crispy topping makes every bite of this French Onion Broccoli Cheese Casserole a delight.

Gourmet Taste with Easy Preparation

While the flavor is undoubtedly gourmet, the preparation of this French Onion Broccoli Cheese Casserole is surprisingly straightforward. We utilize convenience ingredients, such as frozen broccoli florets, which require only thawing and draining, saving valuable chopping time. The cheese sauce, though homemade, follows a simple Béchamel method (melt butter, whisk in flour, add milk), which anyone can master. Plus, this dish is the perfect make-ahead option. You can prepare the entire casserole (minus the final crispy onion topping) up to 24 hours in advance, keeping it covered in the refrigerator until ready to bake. This flexibility makes it an ideal choice for holiday gatherings or busy weeknights when you need a hearty meal ready to go.

For more delicious and easy casserole ideas that are perfect for weeknights or holidays, check out our recipe for Creamy Chicken and Stuffing Casserole.

Why You Should Try This French Onion Broccoli Cheese Casserole Now

If you’re looking for a reason to ditch your standard side dishes and upgrade your comfort food game, the time to make this French Onion Broccoli Cheese Casserole is now. This recipe offers tremendous value in terms of flavor payoff, ingredient quality, and versatility.

A Perfect Marriage of Classic Flavors

The beauty of the French Onion Broccoli Cheese Casserole lies in its innovative fusion. Traditional broccoli casseroles often fall flat, relying on heavy cream of mushroom soup. By contrast, this recipe introduces deep, complex layers. The utilization of high-quality cheeses sharp white cheddar for tang and melty Gruyère for nuttiness combined with that deep beef-broth-infused onion flavor ensures a casserole that tastes truly homemade and sophisticated. This is a dish that appeals to both adults who appreciate complex flavors and children who simply love cheesy, creamy food.

Versatile for Any Occasion

Whether you need a centerpiece for your holiday table or a robust side dish for a simple roast chicken, the French Onion Broccoli Cheese Casserole fits the bill. It holds up beautifully alongside heavy main courses like prime rib, pork roast, or even holiday turkey. Due to its richness, it also works wonderfully as a satisfying vegetarian main course served with a crisp green salad. Because it’s so easy to prep ahead, it alleviates kitchen stress on busy cooking days, making it indispensable for Thanksgiving or Christmas dinners. It pairs wonderfully with other classic, make-ahead comfort sides, such as Easy Crock Pot Sweet Potato Casserole.

The Broccoli Benefit

While this dish is undeniably indulgent, it’s packed with nutrient-rich broccoli. Broccoli is a powerhouse vegetable, providing significant amounts of Vitamin C, Vitamin K, and fiber. By incorporating it into a highly palatable and cheesy dish, you make eating your greens enjoyable for even the pickiest eaters. This recipe uses two full bags of frozen florets, ensuring a hearty serving of vegetables in every scoop. Draining the thawed broccoli well is key here, guaranteeing that the final product is creamy and thick, never watery.

Instagram-Worthy Presentation

Let’s be honest, we eat with our eyes first! The golden-brown crust, the bubbling, gooey cheese, and the vibrant green of the broccoli peeking through the rich sauce make the French Onion Broccoli Cheese Casserole visually stunning. The final flourish of crispy French Fried Onions scattered across the top provides that perfect contrast, signaling to everyone that this is a dish not to be missed. When you bring this bubbly, cheesy bake to the table, be ready for the applause!

Ingredients and Necessary Utensils for French Onion Broccoli Cheese Casserole

Creating this deeply flavorful French Onion Broccoli Cheese Casserole requires focusing on quality ingredients, particularly the cheese and the broth, which are central to the French onion flavor profile. Below is a detailed look at everything you need to execute this recipe perfectly, followed by the essential tools for success.

Detailed Ingredients List for the Casserole

Ensuring you have precise quantities and high-quality ingredients will guarantee the rich, deeply satisfying flavor of this casserole.

For the French Onions:

• Unsalted Butter (4 tablespoons): Used to caramelize the onions. Using unsalted butter allows you to control the overall sodium content of the dish.
• Large Yellow Onions (2): Thinly sliced. Patience is crucial here; these onions must caramelize slowly to develop their signature sweetness and depth, which is the soul of the French Onion Broccoli Cheese Casserole.
• Beef Broth (1/2 cup): Essential for deglazing the pan and infusing the onions with that classic French Onion Soup flavor.
• Dried Thyme (1 teaspoon): Thyme is the traditional herb pairing for French onion flavors, adding an earthy, aromatic note.
• Worcestershire Sauce (1 tablespoon): A secret weapon for deep umami flavor. Its fermented base enhances the savory, meaty notes imparted by the beef broth.

For the Casserole Base and Sauce:

• Frozen Broccoli Florets (2 x 10 ounce bags): Thawed and, most importantly, drained very well. Excess moisture is the enemy of a creamy casserole. Pat them dry with paper towels after thawing to ensure a thick sauce.
• Unsalted Butter (4 tablespoons): Used to create the roux, the thickening base for our creamy cheese sauce.
• All-Purpose Flour (1/4 cup): Combined with butter to form the roux. This is what gives the sauce its smooth, luxurious consistency, ensuring the French Onion Broccoli Cheese Casserole holds its shape.
• Whole Milk (2 cups): Whole milk provides the richest, creamiest texture for the sauce. Lower-fat milk can be substituted, but may result in a slightly thinner consistency.
• Beef Broth (1 cup): This is the remaining broth from the original 1 1/2 cups needed for the whole recipe. Incorporating more beef broth into the Béchamel sauce maintains the savory depth established by the caramelized onions.
• Salt (1/2 teaspoon) and Black Pepper (1/4 teaspoon): Standard seasoning. Always taste and adjust seasoning levels before pouring the sauce over the broccoli.
• Shredded Gruyère Cheese (1 1/2 cups, divided): This nutty, semi-hard Swiss cheese is non-negotiable for authentic French Onion flavor. It melts beautifully and provides a distinct, savory sweetness. You will use 1 cup in the sauce and 1/2 cup for the topping.
• Shredded Sharp White Cheddar Cheese (1 cup): Provides the necessary sharp, tangy contrast to the sweet onions and nutty Gruyère, rounding out the flavor profile of this incredible cheesy broccoli casserole.

For the Topping:

• French Fried Onions (1 x 6 ounce container, divided): The classic crispy topping. Dividing this ensures you have an initial layer for flavor infusion and a final layer for maximum crunch after the cheese has melted.

Essential Tools and Utensils

Having the right equipment ensures smooth preparation and a successful bake.

• 9×13 Inch Casserole Dish: The standard size for this recipe, ensuring proper depth for the creamy filling and surface area for the crispy topping.
• Large Skillet or Dutch Oven: Necessary for the slow and steady caramelization of the onions. A heavy-bottomed pan ensures even heat distribution and prevents scorching.
• Medium Saucepan: Used exclusively for preparing the Béchamel cheese sauce.
• Whisk: Absolutely critical for making the roux and incorporating the milk smoothly to prevent lumps in the cheese sauce.
• Rubber Spatula or Wooden Spoon: For stirring the onions and mixing the final casserole components.
• Measuring Cups and Spoons: For accurate ingredient quantities.
• Colander and Paper Towels: Essential for thoroughly draining and drying the thawed broccoli florets.

If you’re looking for more comforting and easy side dishes, be sure to check out our collection of recipes on our Pinterest board for easy recipes.

Detailed Recipe Steps for the Perfect French Onion Broccoli Cheese Casserole

The success of this French Onion Broccoli Cheese Casserole relies on two key components: perfectly caramelized onions and a flawless, creamy cheese sauce. Follow these steps precisely to achieve a rich and deeply flavored result.

Step 1: Prepare the Caramelized French Onions

1. Melt the Butter: Melt 4 tablespoons of butter in a large skillet or Dutch oven over medium-low heat. Maintaining low heat is vital for true caramelization, not just browning.
2. Caramelize Slowly: Add the thinly sliced yellow onions. Cook, stirring occasionally (about every 3-4 minutes), for 15 to 20 minutes. The onions must become deeply golden brown and soft, shrinking significantly in volume. Patience is key here; do not rush this process, as the deep flavor of the French Onion Broccoli Cheese Casserole comes directly from these onions.
3. Deglaze and Season: Once caramelized, increase the heat to medium. Pour in the ½ cup of beef broth and the Worcestershire sauce. Use a wooden spoon or spatula to vigorously scrape the bottom of the pan, lifting all the sticky, browned bits (known as the fond). This step, called deglazing, adds immense flavor complexity. Stir in the dried thyme.
4. Set Aside: Remove the onions from the heat and set them aside while you prepare the sauce. Keep the remaining 1 cup of beef broth for the sauce.

Step 2: Preheat and Prepare the Broccoli

1. Preheat Oven: Preheat your oven to 375°F (190°C). Lightly grease a 9×13 inch casserole dish.
2. Drain the Broccoli: Ensure the 2 bags of frozen broccoli florets are completely thawed and drained exceptionally well. We cannot stress this enough a watery casserole means failure. Once drained in a colander, gently press them with paper towels to absorb any residual moisture.
3. Place in Dish: Place the thoroughly drained broccoli florets evenly into the prepared casserole dish.

Step 3: Prepare the Velvety Cheese Sauce

1. Make the Roux: In a separate medium saucepan, melt the remaining 4 tablespoons of butter over medium heat. Whisk in the ¼ cup of all-purpose flour. Cook this mixture, stirring constantly, for 1 minute until a smooth, light-colored paste (the roux) forms. Cooking the roux eliminates the raw flour taste.
2. Incorporate Liquids: Gradually whisk in the 2 cups of whole milk. Pour slowly and whisk continuously to ensure the mixture is perfectly smooth and lump-free.
3. Thicken: Bring the milk mixture to a gentle simmer, continuing to whisk frequently. The sauce will begin to thicken slightly as it heats. Reduce the heat to low.
4. Season: Stir in the remaining 1 cup of beef broth, salt, and black pepper. Stir until fully incorporated. Remove the pan from the heat immediately.

Step 4: Add the Cheese and Caramelized Onions

1. Melt the Cheese: Once the sauce is off the heat, stir in 1 cup of the shredded Gruyère cheese and all of the sharp white cheddar cheese. Stir until the cheese is completely melted and the sauce is uniform and smooth. The residual heat from the sauce is enough to melt the cheese perfectly.
2. Combine Flavors: Pour the prepared caramelized French onions and all their liquid (the savory deglazing sauce) into the cheese mixture. Stir well to fully combine the creamy cheese sauce with the deep, savory onion flavors. This is the heart of your French Onion Broccoli Cheese Casserole.

Step 5: Assembly and Initial Bake

1. Coat the Broccoli: Pour the entire cheese and onion mixture evenly over the broccoli in the casserole dish. Gently stir the mixture using a rubber spatula to ensure every floret is thoroughly coated in the rich, cheesy sauce.
2. First Topping Layer: Sprinkle the remaining ½ cup of Gruyère cheese evenly over the top of the casserole. This cheese layer will melt into a delicious, bubbly crust.
3. Crispy Start: Scatter half (about 3 ounces) of the French Fried Onions over the cheese layer.
4. Initial Bake: Bake for 20 to 25 minutes, or until the casserole is bubbling hot throughout and the cheese is beautifully melted and lightly golden.

Step 6: The Finishing Touch for Crunch

1. Remove and Adjust Heat: Carefully remove the casserole from the oven. Increase the oven temperature to 400°F (200°C).
2. Add Final Topping: Scatter the remaining French Fried Onions evenly over the top of the hot casserole. This second layer ensures maximum crispness.
3. Final Baking: Return the French Onion Broccoli Cheese Casserole to the oven and bake for an additional 3 to 5 minutes, or until the topping is golden brown and perfectly crisp. Watch carefully during this stage to prevent scorching.
4. Rest and Serve: Allow the casserole to rest for 5 to 10 minutes before serving. This resting period allows the sauce to fully set, ensuring perfect scoops.

Tips, Variations, and Pro Advice for French Onion Broccoli Cheese Casserole

Mastering this rich French Onion Broccoli Cheese Casserole is simple, but a few professional tips can ensure perfection every time. Plus, we offer delicious variations for dietary needs and flavor experimentation.

Essential Tips to Avoid Common Mistakes

Preventing a Watery Casserole

The single most common mistake in broccoli casseroles is excessive moisture, which results in a thin, disappointing sauce. Because this recipe uses frozen broccoli, it retains significant water when thawed.

• Draining is Non-Negotiable: After thawing the broccoli, drain it in a colander. Then, spread the florets on a few layers of paper towels and pat them vigorously to wick away as much moisture as possible.
• Thickening the Sauce: Ensure your roux is cooked for the full minute and that your sauce simmers long enough to thicken slightly before the cheese is added. The ratio of flour to liquid in this recipe is designed for a perfect, thick consistency for your French Onion Broccoli Cheese Casserole.

Achieving the Perfect Caramelization

The caramelized onions are the star flavor. Don’t try to cook them quickly over high heat. High heat will burn the edges before the sugars have a chance to properly develop. Keep the heat on medium-low and dedicate the full 15-20 minutes, stirring occasionally, until the onions are soft, jammy, and deeply colored.

Delicious and Easy Ingredient Variations

Cheese Substitutions

While Gruyère is traditional for French Onion Broccoli Cheese Casserole, you have options:

• If Gruyère is unavailable: Substitute with shredded Swiss cheese (Emmenthaler) or Fontina. Both offer good melting properties and a similar nutty flavor profile.
• For Extra Sharpness: Swap the white cheddar for an extra sharp yellow cheddar or a blend of Monterey Jack and sharp Provolone.

Broccoli Alternatives

You can easily substitute the broccoli with other vegetables for variety:

• Broccoli/Cauliflower Blend: Use one bag of frozen broccoli and one bag of frozen cauliflower florets.
• Fresh Broccoli: If using fresh broccoli, cut the florets and quickly blanch them (boil for 2 minutes, then plunge into ice water) to ensure they cook through during the bake. Pat dry thoroughly before adding to the casserole dish.

Meat and Protein Additions

To turn this side dish into a complete main course, stir in cooked protein:

• Chicken or Turkey: Add 2 cups of shredded rotisserie chicken or leftover turkey breast (perhaps from your perfectly seasoned Turkey Brine efforts!) directly into the sauce before pouring it over the broccoli.
• Bacon: Crumble 6-8 slices of crispy bacon over the top along with the final onion layer for a smoky flavor addition.

Dietary and Lifestyle Modifications

Gluten-Free French Onion Broccoli Cheese Casserole

Making this casserole gluten-free is straightforward:

• Roux Substitute: Replace the all-purpose flour with a 1:1 gluten-free flour blend, or use cornstarch. If using cornstarch, mix 2 tablespoons of cornstarch with a splash of cold milk before adding to the simmering whole milk, then whisk until thickened.
• Topping Check: Most French Fried Onions are naturally gluten-free, but always check the label, or make your own crispy fried onions using gluten-free breading.

Making It Ahead and Freezing

• Make Ahead: Prepare the casserole completely through Step 6 (before adding the crispy onion topping). Cool slightly, cover tightly with plastic wrap and foil, and refrigerate for up to 24 hours. When ready to bake, remove from the fridge 30 minutes prior, then bake as directed (you may need an extra 5-10 minutes if baking straight from cold). Add the crispy onions during the last 5 minutes.
• Freezing: Casseroles containing roux and cheese sauces generally freeze well. Assemble the casserole fully (without the crispy onions). Wrap tightly and freeze for up to 3 months. Thaw overnight in the refrigerator before baking. Note that the texture of the sauce may slightly change upon reheating but will still be delicious.

Nutritional Values and Benefits of French Onion Broccoli Cheese Casserole

While the French Onion Broccoli Cheese Casserole is classified as rich comfort food due to its butter and cheese content, it also offers substantial nutritional benefits from its core ingredients. It’s a well-rounded dish providing a balance of macronutrients and essential vitamins.

Estimated Nutritional Breakdown (Per Serving)

Given the generous use of whole milk, butter, and two types of cheese, this casserole is nutrient-dense. Since precise nutritional data would require laboratory analysis, the following estimates are based on typical ingredient composition (assuming 8 servings):

• Calories: Approximately 450–550 kcal
• Protein: 20–25g (High due to milk and cheese, supporting muscle maintenance and satiety.)
• Total Fat: 35–45g (Primarily saturated fats from butter and cheese, contributing to the dish’s flavor and richness.)
• Carbohydrates: 15–20g (Mainly from the flour in the roux, the onions, and the broccoli.)
• Fiber: 3–5g (Provided primarily by the broccoli.)

This casserole functions as a hearty, filling side or a standalone main course, providing a substantial amount of protein and fats necessary for sustained energy.

Health Benefits of Key Ingredients

Broccoli: The Green Powerhouse

Broccoli is the anchor vegetable in this French Onion Broccoli Cheese Casserole, bringing significant health advantages:

• Vitamin K: Broccoli is exceptionally high in Vitamin K, which is vital for blood clotting and bone health.
• Vitamin C: A strong source of Vitamin C, supporting immune function and collagen production.
• Fiber: The high fiber content aids in digestive health and helps stabilize blood sugar levels.

Even when baked into a creamy sauce, broccoli retains much of its nutritional value, making this casserole a delicious way to boost your vegetable intake.

Dairy and Cheese: Essential Nutrients

The whole milk, Gruyère, and sharp white cheddar contribute essential nutrients:

• Calcium: Cheese and milk are excellent sources of calcium, necessary for bone density and strength.
• Protein: Dairy products provide high-quality protein, which is vital for tissue repair and growth.
• Healthy Fats: While rich, the fats in dairy help in the absorption of fat-soluble vitamins (A, D, E, K), ensuring the nutrients in the broccoli are utilized efficiently by the body.

Caramelized Onions: Antioxidants and Prebiotics

The base flavor of this French Onion Broccoli Cheese Casserole is the onion, which offers more than just flavor:

• Antioxidants: Onions contain powerful antioxidants, including quercetin, which help fight free radicals in the body.
• Prebiotics: Onions are a source of prebiotics, promoting a healthy gut biome and supporting digestive health.

In summary, while this is an indulgent comfort dish, the combination of nutritious vegetables and dairy ensures that you are consuming a well-balanced array of vitamins and minerals alongside a fantastic flavor profile.

FAQs About French Onion Broccoli Cheese Casserole

Do you have questions about perfecting your French Onion Broccoli Cheese Casserole? Here are some of the most common inquiries related to this ultimate comfort food side dish.

Conclusion: The Ultimate Comfort Food Side Dish Reimagined

The French Onion Broccoli Cheese Casserole is more than just a side dish; it’s a celebration of comfort food elevated by gourmet flavors. We’ve taken the beloved creamy broccoli bake and infused it with the deep, savory, and caramelized soul of classic French Onion Soup. From the patient preparation of those sweet, golden onions to the creation of the silky, Gruyère-laced cheese sauce, every step in this recipe is designed to maximize flavor and create an unforgettable culinary experience.

The satisfying contrast between the tender, nutrient-packed broccoli and the gooey, nutty cheese, finished with that perfect, golden crunch of French fried onions, ensures this dish will disappear fast. Whether you are hosting a festive holiday dinner or simply seeking a spectacular meal to warm your family on a cold night, this casserole delivers on every promise of richness and flavor.

We encourage you to dedicate the time to properly caramelize those onions it truly makes all the difference in achieving that signature French Onion Broccoli Cheese Casserole taste. Once you try this recipe, you’ll realize that the days of bland, cream-of-soup casseroles are officially over. This is the new standard for cheesy broccoli excellence.

We hope you love preparing and sharing this recipe as much as we do. If you try the French Onion Broccoli Cheese Casserole, let us know what you think in the comments below! Don’t forget to share this recipe with friends and family who appreciate the finer things in comfort food.

# French Onion Broccoli Cheese Casserole

A rich and creamy casserole blending the savory, umami depth of classic French onion soup with tender broccoli florets and a decadent blend of Gruyère and sharp white cheddar cheeses.

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Prep Time 15 minutes mins

Cook Time 45 minutes mins

Total Time 1 hour hr

Course Main Course, Side Dish

Cuisine American, French-inspired

Servings 6 servings

Calories 445 kcal

Equipment

• Large skillet or Dutch oven
• 9x13 inch Casserole Dish
• Medium saucepan
• Whisk

Ingredients

  

For the French Onions

• 4 tablespoons unsalted butter
• 2 large yellow onions thinly sliced
• 1/2 cup beef broth
• 1 teaspoon dried thyme
• 1 tablespoon Worcestershire sauce

For the Casserole Base and Sauce

• 2 (10 ounce) bags frozen broccoli florets thawed and drained well
• 4 tablespoons unsalted butter
• 1/4 cup all-purpose flour
• 2 cups whole milk
• 1 cup beef broth remaining from onion preparation
• 1/2 teaspoon salt
• 1/4 teaspoon black pepper
• 1 1/2 cups shredded Gruyère cheese divided
• 1 cup shredded sharp white cheddar cheese

For the Topping

• 1 (6 ounce) container French Fried Onions divided

Instructions

 

Prepare the French Onions

• Melt 4 tablespoons of butter in a large skillet or Dutch oven over medium-low heat. Add the sliced yellow onions and cook, stirring occasionally, for 15 to 20 minutes, until deeply golden brown and caramelized.
• Increase the heat to medium and pour in the 1/2 cup of beef broth and the Worcestershire sauce, scraping the bottom of the pan to lift any browned bits (deglazing). Stir in the dried thyme. Set the onions aside.

Prepare the Base and Sauce

• Preheat oven to 375°F (190°C). Lightly grease a 9x13 inch casserole dish. Place the drained broccoli florets into the prepared casserole dish.
• In a separate medium saucepan, melt the remaining 4 tablespoons of butter over medium heat. Whisk in the flour and cook for 1 minute, stirring constantly, until a smooth paste (roux) forms. Gradually whisk in the 2 cups of whole milk until the mixture is smooth.
• Bring the milk mixture to a gentle simmer, whisking frequently. Once the sauce has thickened slightly, reduce the heat to low. Stir in the remaining 1 cup of beef broth, salt, and black pepper. Remove the pan from the heat.
• Stir in 1 cup of the Gruyère cheese and all of the sharp white cheddar cheese until completely melted and the sauce is smooth. Pour the prepared caramelized French onions and their liquid into the cheese sauce. Stir well to combine.

Assembly and Baking

• Pour the entire cheese and onion mixture over the broccoli in the casserole dish. Gently stir the mixture to ensure the broccoli is evenly coated.
• Sprinkle the remaining 1/2 cup of Gruyère cheese evenly over the top of the casserole. Scatter half (about 3 ounces) of the French Fried Onions over the cheese layer.
• Bake for 20 to 25 minutes at 375°F, or until the casserole is bubbly and the cheese is melted.
• Remove the casserole from the oven. Increase the oven temperature to 400°F (200°C). Scatter the remaining French Fried Onions over the top. Return the casserole to the oven and bake for an additional 3 to 5 minutes, or until the topping is golden brown and crisp.
• Allow the casserole to rest for 5 to 10 minutes before serving.

Notes

For a richer flavor, consider using fresh thyme instead of dried. If you prefer a milder cheese flavor, substitute the sharp white cheddar with mozzarella or Provolone, which melt beautifully but lack the necessary tang to cut through the richness of the French onions.

Keyword broccoli, cheesy casserole, comfort food, french onion, gruyère