Sift the flour with the powdered sugar and salt, add the cold butter pieces, chop with a knife, and rub in by hand into fine crumbs. Beat in the egg and knead the dough.

Place a parchment circle on the bottom of the pan. Roll out the dough, line the pan, form tall sides, and prick the bottom with a fork. Chill for 30 minutes.

Wash, peel, and slice the apples. Mix the eggs, sour cream, and poppy seed filling with a mixer until smooth.

Preheat the oven. Pour the poppy seed filling into the chilled base and arrange the apple slices on top. Bake for 10 minutes at 160°C.

While the pie is in the oven, whip the eggs with the sugar until pale and fluffy, sift in the flour, cornstarch, and baking powder, add the vanillin, and fold in gently.

Remove the pie, pour the sponge batter on top, and continue baking for 30-40 minutes at 160-170°C.

Let the finished pie cool completely and dust with powdered sugar. Enjoy!