For the dough, knead the first 4 ingredients into a smooth dough. Divide into 2 equal pieces and refrigerate.
For the topping, peel, core and coarsely grate the apples, add sugar to taste. Roast the hazelnuts (without additional fat) in the pan and let them cool. Before the apples come on the batter, squeeze out the juice and drain. If necessary, add sugar and add the cinnamon.
Roll out the dough into 2 evenly thick sheets of dough. Carefully line the greased baking pan with a sheet of pastry, pierce holes with a fork and sprinkle with half of the roasted hazelnuts. Spread the apples evenly on top. Sprinkle the second half of the nuts on top and cover with the rest of the pastry. Prick holes at the top with the fork.
Bake in the preheated oven at approx. 160 - 180 degrees until the cake is golden brown. Dust with icing sugar while it is still warm.