Grease a 13 by 9 pan and and pour Caramel Sauce (1/2 cup) on the pan and distribute the sauce evenly on the pan. Set aside. Take a large mixing bowl and add Butter (1/2 cup), Granulated Sugar (1 cup) and mix it together. Then, add Egg (3), Vanilla Extract (2 teaspoon) and whisk it together.
Mix All-Purpose Flour (2 cup) and Salt (1 teaspoon), Unsweetened Cocoa Powder (1/2 cup), Baking Powder (2 teaspoon), Baking Soda (1 teaspoon) together. Sift the dry ingredient into the butter mixture half at a time. Incorporate with Buttermilk (1 cup). Pour the batter into the pan. Smooth out and set aside
Pour Egg (5), Evaporated Milk (12 fluid ounce), Sweetened Condensed Milk (14 ounce) and Vanilla Extract (1 teaspoon) into a blender and blend it together. Pour this mixture on top of the batter in the pan. Cover with foil.
Take a bigger pan, put the cake pan into it and fill with hot water until it reaches half of the pan. Preheat the oven to 350 degrees F (180 degrees C) and bake for 1 to 1.5 hours. Let it cool completely. Once cool, place a large plate over top and flip it over to release the chocoflan.