Whip butter, sugar, vanilla sugar and eggs until creamy (make sure that the butter and eggs are at room temperature, because the dough will curdle if the ingredients are too cold). Add the lemon juice, stir in the flour mixed with baking powder.
Pour the dough into a greased springform pan (diameter 26 cm). Peel, quarter and score the apples and place on the dough. Baking: convection (hot air) 150 - 170 ° C, 45-55 min.
After cooling, cover with powdered sugar or mixed jam.