Spray a 12-cup Bundt cake pan with cooking spray. In a small bowl, whisk together flour, cocoa, baking soda, and salt. Set aside.

Add butter and chocolate to a microwave-safe bowl. Microwave for 2 minutes at 50% power, or until melted.

Add buttermilk, sugar, eggs, and vanilla to the chocolate. Whisk until combined.

Stir in the flour mixture until just combined. Pretend that this picture is of flour, not buttermilk.

Pour the caramel sauce into the bottom of the pan.

Spread the batter over the caramel layer.

Blend sweetened condensed milk, milk, cream cheese, eggs, yolks, and vanilla for 1 minute.

Pour flan over cake batter. Place the cake pan in a roasting pan.

Pour boiling water halfway up the sides of the cake pan.

Bake for 75 to 90 minutes, a toothpick will come out clean, or you can take an internal temp, it should register 180 degrees.

Transfer the cake to a wire rack. Let come to room temperature, transfer to fridge, and chill for at least 8 hours. To unmold, dip the bottom of the cake pan in hot water for one minute. Place the cake plate over the cake pan and flip over. The cake will release and the caramel will drip down the sides.