Separate the eggs. Mix the egg yolks with the butter and sugar until frothy. Stir in the quark, semolina, baking powder and lemon zest. Add the plums to the mixture. Beat the egg whites until stiff and carefully fold them into the plum quark.
Grease a round baking dish a little, pour in the plum quark, sprinkle with flaked almonds and sugar and put flakes of butter on top. Bake in the preheated oven at 200 ° C top / bottom heat for approx. 20 minutes until the casserole is light brown.