Stir the butter until foamy, then stir in the sugar and egg yolks. Now alternately stir in the sifted flour mixed with the baking powder and the milk. Finally fold in the stiffly beaten egg whites. Pour the batter into a well-greased springform tin sprinkled with crumbles or ground almonds. Then place the apple wedges lightly on the dough (do not press in!). Bake at 180 - 200 ° for approx. 45 minutes.