Mix the butter, sugar and vanilla sugar until frothy. Gradually stir in the eggs well one by one.
Peel the bananas, mash them finely with a fork and stir in with the whipped cream and rum. Mix cocoa powder, flour, baking powder and desiccated coconut and fold in.
Pour the dough into a greased bundt cake pan and bake at 180 degrees for about 50-60 minutes.