In a big bowl, combine the flour, salt, sugar, vanilla sugar. Grate the butter and combine with flour with your fingertips until remains only small peas.
In a small bowl, lightly whisk the egg with a fork. Add to the dough and mix until forms a rough ball (don't knead it). Rest in the freezer for about 15 min.
Meanwhile, in a bowl lightly whisk the quark, eggs, sugar, vanilla sugar, starch. Add the apples and combine.
Preheat oven to 180 C temp. Grease the baking pan (20×25 cm) with butter.
Remove the dough from the freezer. Grate it. Add 2/3 of the dough to the baking pan and press with your fingers to even out.
Pour the filling on the dough. Add the apple jam on the top, spread over the filling.
Add remained dough on top.
Bake about 1 hour. Remove from a pan when completely cool. Dust with sugar powder.