Grease a fat pan (approx. 32 x 39 cm; deep baking tray). Put the cookies in a freezer bag, roll over them several times with a cake roll and crumble them. With your hands, knead 150 g butter, 3 tbsp. flour and biscuit crumbs into crumbles.
Preheat oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer).
Cream 175 g butter, sugar, vanilla sugar and 1 pinch of salt with the whisks of the mixer. Stir in the eggs one by one. Stir in 500 g flour, baking powder, cinnamon and 300 g applesauce.
Spread the dough smoothly on the fat pan. Spread the remaining applesauce on top and sprinkle with the crumbles. Bake in the oven for about 40 minutes. Let it cool down. Vanilla ice cream tastes good with it.