Mix the margarine with the sugar and vanilla sugar until frothy. Gradually stir in the eggs. Mix the flour and baking powder, stir in a spoonful.
Peel the apples, cut into eighths and divide again.
Grease a springform pan and pour in half of the batter. Spread the apple pieces on the dough. Stir 1 tablespoon of cocoa into the other half of the batter. Now put the dough on the apples and smooth out.
Bake in the oven at 180 ° C (convection) for about 50 minutes. Dust with icing sugar after cooling.