Preheat oven: Preheat oven to 350°F.Prep the pan: Spray an angel food cake pan or a 12 cup bundt pan (without a removable bottom) with cooking spray generously. Pour the caramel sauce evenly over the bottom of the pan.
Combine the dry ingredients: In a medium bowl combine the flour, cocoa, cinnamon, baking soda, salt and mix; set aside. In a microwave safe bowl and the chocolate and butter and microwave in 30 seconds intervals until chocolate is melted and it's smooth. Mine took about 1 minute and 30 seconds.
Combine the wet ingredients: Add buttermilk, sugar, eggs and vanilla to the melted chocolate and whisk until it's smooth. Pour chocolate mixture to the dry ingredients and whisk until it well incorporated and smooth. Pour the chocolate batter evenly over the caramel in the cake pan.
Prepare the flan: To make the flan simply add all the flan ingredients to a blender and process on low until smooth. Be careful, there's a lot of batter here, so you want to make sure you do this on low otherwise it might explode all over. Pour the flan batter over the chocolate in the pan.
Bake the cake: Place the cake pan in a large roasting pan and place it in the oven. Add enough hot water to the roasting pan to reach halfway up the sides of the pan. Careful so you don't burn yourself. Bake the cake for about 1 hour and 30 minutes, mine took about 1 hour and 40 minutes, or until you insert a toothpick in the cake and it comes out clean.
Finish the cake: Cool the cake in the pan for about 15 minutes then carefully invert onto a cake platter. Cool completely at room temperature then chill for at least 4 hours before slicing and serving.