Quickly knead the ingredients for the shortcrust pastry together, wrap in foil and put in the refrigerator for 1/2 hour.
For the crumble, put the butter, sugar and flour in a bowl and stir with a dough hook until you get the crumble. Chill the crumble until you need it.
For the topping, stir the butter, sugar and vanilla sugar until soft. Add the eggs. Add the quark, the juice of half a lemon and the flour. Press the dough into a 26 cm diameter springform pan. Put the quark mixture on top and spread the apple pieces over it. Press the apple pieces lightly into the curd mixture. Sprinkle the crumble on the cake.
Preheat the oven to 170 ° C and bake the cake for about 60 minutes.