Mix the flour well with baking powder, baking soda, salt, custard powder and cocoa.
Beat eggs with sugar and vanilla sugar until lightly creamy. Melt the butter and carefully stir in with the sour cream and milk. Carefully and briefly stir in the flour mixture and finally stir in the chopped chocolate chips.
Now fill 3/4 of the dough into molds and bake at 190 ° C top / bottom heat for 20-25 minutes.