Preheat your oven to 350°F (175°C). Thoroughly grease a standard 12-cup muffin tin with non-stick cooking spray or butter. Ensure the sides and bottoms of the cups are completely coated to prevent sticking.

Ensure the 6 slices of bacon have been cooked until very crispy, then blot away excess grease and crumble them into small, bite-sized pieces. Set aside.

In a large mixing bowl, crack all 12 large eggs. Add the heavy cream (or milk), salt, and black pepper to the bowl.

Whisk the mixture vigorously for 1 to 2 minutes until the eggs are fully incorporated, slightly frothy, and a uniform light yellow color. Aerating the eggs helps achieve maximum fluffiness.

Gently fold the shredded cheddar cheese, the crumbled bacon pieces, and the optional chopped chives into the egg mixture. Ensure the solids are evenly distributed.

Carefully pour the egg mixture into each prepared muffin cup, filling them evenly about three-quarters of the way full. Do not overfill.

Bake for 20 to 25 minutes at 350°F (175°C). The egg bites are done when they are set, puffy, lightly golden around the edges, and a toothpick inserted into the center comes out clean.

Remove the muffin tin from the oven and allow the egg bites to cool in the pan for 3 to 5 minutes. Use a small offset spatula or butter knife to gently loosen the edges before transferring them to a serving plate.