Pre heat oven to 160oC
Find a roasting tray with high sides that the bunt pan will fit into, so that the Chocoflan can be cooked in a bain maire (water bath) set up.
Place the bundt tin in the oven to get warm.
If you choose to make the caramel, place the sugar in a sauce pan over medium heat, do not stir but allow to melt, swirl to incorporate all the sugar and when as dark as you like take off the heat. Remove the bundt from the oven and pour the caramel into the base, swirling to coat. Allow to harden. When cool and hard, grease the inside of the pan with butter, where the caramel has not stuck.
To make the cake, sift the flour, baking powder and soda, cocoa powder and salt to a bowl whisk to combine. In another bowl, with an electric hand beater, cream the butter and the two sugars until pale and fluffy, add the eggs one at a time and incorporate thoroughly. Mix the coffee and the butter milk to gather is a jug. Add 1/3 of the flour mix to the butter and 1/2 the milk mix and beat together, add another 1/3 flour mix and the rest of the milk and beat, then fold in the rest of the flour until incorporated and smooth. Pour into the bundt tin and smooth out the top with a spatula.
To make the flan, put everything except the eggs into a blender or a jug suitable for a stick blender, blend until well combined, then add the eggs and blend for 30 seconds or so.
Carefully ladle the flan mix on the top of the cake mix. Grease a piece of foil large enough to cover the bundt and loosely tuck around the sides. Place carefully in the roasting pan and fill with boiling water to 2-3cm up the side of the bundt tin.
Bake for 1 hour - test to see if done by inserting toothpick, it should come out almost clean. Then remove from water bath, remove foil and allow to cool completely for an hour. Invert onto a dish and refrigerate until well chilled, at leat 2 hours. Can be made the day before too. When slicing remember to wipe the crumbs off the knife after each slice so that flan remains clean.