For the crumble, put the flour, marzipan, sugar, butter (cut into small pieces) and a little cinnamon in a bowl. Use the dough hook of the mixer or your hands to make crumbles. Then add the almond flakes and mix in. Refrigerate.
For the dough, stir together the butter, sugar and vanilla sugar until frothy. Gradually stir in the eggs well one by one. Mix the hazelnuts, flour and baking powder together and mix in with the milk and amaretto. Place the dough on a greased baking sheet and smooth it out. Wash, halve and core the plums. Cover the dough tightly with it and then spread the crumble over it.
Bake in the preheated oven at 180 degrees for about 45 minutes.