Preheat oven to 325°F.

Make the caramel sauce. Pour the sugar into a medium skillet or saucepan over medium heat, stirring constantly. The sugar will start to clump together and turn a light brown color. Continue stirring until it has fully melted into a syrup-like consistency and reaches a golden brown color, creating a caramel.

Working quickly, take the caramel off the heat and pour it into a 9-inch round cake pan, evenly coating the bottom and sides of the pan. Set the pan aside to allow the caramel to harden.

Make the chocolate flan mixture. Whisk the eggs together in a medium bowl until fully combined. Set aside. In a separate large bowl, pour in the sweetened condensed milk and set aside.

Heat the milk and heavy cream in a medium saucepan over medium heat until scalding, about 175°F, making sure to stir occasionally. Remove from the heat and whisk in the bittersweet chocolate chips and cocoa powder until everything is fully combined.

Carefully pour the chocolate mixture into the bowl of sweetened condensed milk. Whisk until fully combined.

Slowly pour the beaten egg mixture into the chocolate mixture and whisk slowly until the eggs are fully incorporated. Whisk gently to reduce the number of air bubbles in the flan.

Once the caramel has hardened, pour the chocolate flan mixture into the cake pan. Cover with aluminum foil and carefully place it in the middle of a large roasting pan or baking dish.

Prepare a water bath for the flan by pouring 4-6 cups of boiling water into the roasting pan so that it reaches halfway up the cake pan.

Carefully place the roasting pan in the center rack of the oven and bake for 1 hour.

Remove the baking dish from the oven and take the cake pan out of the water bath. Remove the aluminum foil and check to make sure the flan is fully cooked. The flan should be slightly jiggly, like jello. If the middle of the flan is still liquidy, bake for an additional 5-10 minutes.

Allow the flan to cool at room temperature for 1 hour before refrigerating for at least 4 hours, but preferably overnight.

To serve, slide a knife along the edges of the pan to loosen up the flan. Place a plate on top of the flan, grab hold of both the plate and the pan, and quickly flip it over so that the flan is now upside down. Carefully lift off the cake pan. Your flan should be sitting in the caramel on the plate.

Slice the flan and serve with the rich caramel sauce.