For the dough, work the flour, butter, sugar, egg and vanilla sugar into a dough and spread it with your hands on a baking tray lined with baking paper. Press up an edge of approx. 5 - 6 cm.
Now peel the apples, cut into small pieces and mix with the applesauce in a bowl. Spread the mixture on the dough.
Then bake in the preheated oven on the middle rack at 180 ° C for about 25 minutes.
In the meantime, prepare the streusel. Knead the flour, sugar, butter, chopped walnuts and cinnamon with your hands to make crumbles.
After 25 minutes, take the cake out of the oven briefly, spread the crumble on top and bake for another 25 minutes at 180 ° C fan oven.
If you like, you can dust the cake with powdered sugar before serving.