Heat your oven to 350°F (176°C). Grease a 12 cup (2.8lt) ring or Bundt cake mold with the 2 tbsp. (28g) unsalted butter (Non-stick pans should be well greased also.) Drizzle in the butterscotch or caramel sauce. Set the pan aside.

In a large bowl, combine the flour, cocoa, baking soda, baking powder and salt. Set aside.

In the bowl of a mixer, combine the butter, sugar, egg and egg yolk. Beat until well combined and fluffy, about 2 minutes. Add the egg and egg yolk and beat for another 30 seconds. Alternately add portions of the flour mixture and the buttermilk to the mixer and beat over slow speed until all the ingredients combined, about 2 minutes over medium speed. Pour into the prepared pan.

To make the flan, combine all of the remaining ingredients in a blender and blend until smooth. Pour the mixture into the prepared baking pan on top of the cake batter. Do not mix together. Flan mixture will automatically migrate to top of cake while baking.

Cover the filled cake pan with a sheet of heavy aluminum foil. Place cake pan inside of a roasting pan. Make a water bath for baking your chocoflan cake by placing the prepared cake pan in a larger roasting pan with 1” (2.5cm) of hot water. Place both pans in the preheated oven and bake for 80 minutes.

Remove the cake pan from the oven and allow to cool completely for at least 3-5 hours.

Carefully run a knife around the outer edges of the ring pan and around inner ring. Invert the cake onto a serving platter. Drizzle with the extra butterscotch sauce, cajeta, thin dulce de leche, or caramel sauce.