For the dough, first stir the butter or margarine with the sugar until frothy. Mix in the eggs one by one. Mix the flour, cocoa and baking powder together, sift over the butter mixture and stir in.
For the cream, bring the milk to the boil. Mix the custard powder with the vanilla sugar and some of the milk and pour the mixture into the milk. Bring to the boil while stirring and allow to cool.
For the crumbles, knead the flour, sugar and butter until you get small crumbles.
Grease the baking sheet or line it with parchment paper and spread the dark dough evenly over it. Spread the pudding cream on the dough and use a spoon to make a pattern. Sprinkle the sprinkles over the cake.
Bake the cake in a preheated oven at 170 ° C for about 30 minutes.