For the base: cut flour, 170 g sugar, butter into small pieces, put vanilla sugar and baking powder in a bowl, knead everything well and spread on a baking sheet and press down well.
Peel the apples, cut in half, core, quarter and cut into thin slices. Mix with lemon juice and spread the bottom.
Heat the milk in a saucepan. Cut the marzipan into small pieces and allow to dissolve in the milk. Separate the eggs. Beat the egg whites with a pinch of salt until stiff. Whisk the remaining sugar (80gr.), Cream and custard powder. Bring the marzipan milk to the boil. Add the egg yolk mixture while stirring and bring to the boil again, let cool down a little. Fold in the egg whites.
Spread the marzipan pudding cream on the apples and smooth out. Bake the apple and marzipan sheet cake in a hot oven at 180 degrees for about 45-50 minutes.