For the crumble apple cake, mix soft butter with brown sugar and vanilla sugar until homogeneous.
Sift flour, baking powder and cornstarch and fold in. Finally, add eggs and flavoring to the mixture and mix well.
Pour into a greased springform pan. Peel apples and spread in wedges on the dough. Preheat oven to 180 °C top/bottom heat.
For the crumble, mix flour, butter, sugar, vanilla sugar and cinnamon and sprinkle on the cake. Bake the crumble apple cake for 40-45 minutes.