Put the flour, sugar, egg yolk, lemon juice, finely chopped butter, baking powder and vanilla sugar in a bowl. Process into sprinkles with your fingertips. Chill briefly.
Butter a springform pan (28 cm) well. Fill in half of the crumble and press firmly. Beat the butter until frothy. Add the sugar, vanilla sugar, semolina, lemon zest and egg yolk. Mix everything well. Mix in the quark.
Beat the egg whites until stiff. Draw under the curd mixture. Pour this cream over the crumble and smooth it out. Cover with the remaining sprinkles. Bake at 180 degrees for 60 minutes.