First separate the eggs and beat the egg whites with a pinch of salt and about 50 g of sugar until stiff. For the dough, mix the egg yolks, flour, butter, sugar, quark, cornstarch, baking powder and vanilla sugar thoroughly. Egg whites under lift. Grease a baking sheet (about 25 cm X 40 cm) with butter and dust with flour. Spread the dough evenly on top and generously cover with plums and sprinkle with a little sugar.
Mix the ingredients for the crumble and spread over the plum cake. Bake for about 50 minutes on the middle rack in the oven preheated to 180 degrees.