Grease a springform pan (26 cm diameter) and line the bottom with baking paper. Peel, core and quarter or sixth the apples, drizzle with a little lemon juice.
Beat the butter, powdered sugar, vanilla sugar and egg yolks until lightly creamy. Beat the egg whites with a pinch of salt. Mix sugar and cornstarch and gradually add and beat until stiff. Fold the egg whites with the flour and baking powder into the butter mixture. Spread the mixture in the pan and spread the apples on top.
Pre-bake in a preheated oven at 175 ° C for approx. 10 minutes. In the meantime, make the crumble. To do this, knead butter, sugar, flour, nuts, cinnamon and salt into crumble. Spread these on the cake and bake in 30-35 minutes.