Preheat your oven to 350°F (175°C). Grease a 9-inch (23cm) springform pan and set aside.

In a mixing bowl, combine the granulated sugar and melted butter. Stir until well combined.

Add the eggs and vanilla extract, mixing until smooth.

Sift in the cocoa powder, flour, salt, and baking powder. Stir until just combined, being careful not to overmix.

Pour the brownie batter into the prepared springform pan. Spread it evenly across the bottom.

Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. Remove from the oven and let cool.

In a large mixing bowl, beat the softened cream cheese until smooth and creamy.

Gradually add the granulated sugar, mixing until fully combined.

Add the eggs, one at a time, mixing well after each addition.

Mix in the vanilla extract, fresh lemon juice, and lemon zest until the mixture is smooth and well combined.

Pour the lemon cheesecake filling over the cooled brownie crust in the springform pan. Smooth the top with a spatula.

Bake in the oven for 50-60 minutes, or until the edges are set but the center still has a slight jiggle.

Turn off the oven and leave the cheesecake in the oven with the door slightly ajar for 1 hour to cool gradually.

After the cheesecake has cooled to room temperature, refrigerate for at least 4 hours, or preferably overnight, to set completely.

Once chilled, carefully remove the sides of the springform pan. Slice the cheesecake and serve with whipped cream, lemon slices, and fresh mint leaves if desired.