For the base, mix the flour and baking powder together, pile up. Make a well in the middle of the flour mixture, add the egg, sugar and vanilla sugar, stir, distribute the flakes of butter on the edge and knead from the outside to form a dough.
Line a greased springform pan, dusted with non-slip flour, with the dough, pull up the edge approx. 3 cm. Spread the fruit (peel apples and cut into thin slices) on the base and bake at 200 ° C for about 15 minutes.
For the topping, beat the eggs well with sugar, vanilla sugar, lemon juice, sour cream and cornstarch. Put on the pre-baked base. Bake at 200 ° C for another 45 minutes.