Spray tray with cold tap water. Place thawed puff pastry slices close together on it. Mix egg yolk with tap water. Brush the dough with it, leaving the edges free.
For the crumble, mix butter, flour, sugar, vanillin and cinnamon with the whisk of a hand mixer. With wet hands, arrange crumbles and sprinkle on top of dough. Put in the oven, set to 200 degrees Celsius and bake for 35 minutes. Let cool briefly and split into pieces with a serrated knife.
Assemble two Prasselkuchen leaves with whipped cream or vanilla cream, if desired.
Tip: Cinnamon gives dishes a wonderful sweet and spicy note!