Mix the egg and quark together. Add lemon juice, sugar, vanilla sugar and margarine / butter. Stir everything until foamy. Mix flour with baking powder and pour in.
Put the dough in a greased springform pan (26cm). Place the plums on top in a circle so that they stand in the batter. Sprinkle with flaked almonds and bake at 180-200 degrees (you have to try) for 50-60 minutes. The dough should be nicely browned, but the plums shouldn`t be burnt. Suck off excess juice, especially from the middle, with kitchen paper.
The cake tastes almost even better the next day, if it has been pulled through a little.