1. Preheat the oven to 150°C fan (170°C upper and lower heat). Beat the egg whites until stiff, slowly adding half the sugar in a stream and continuing to beat until the whites remain in stiff peaks. Whip the egg yolks with the remaining sugar, vanilla sugar and lemon zest until thick and creamy. Stir in the low-fat ricotta, cornflour and semolina until smooth, then carefully fold in the beaten egg whites.
2. Brush heat-resistant dessert glasses with butter. Fill 1-2 tbsp of the quark mixture into each glass and place 3 prunes on top. Fill with the rest of the quark mixture, sprinkle with almonds and drizzle with the remaining butter.
3. Place a fairly deep baking dish or roasting tin on the rack in the oven, place the glasses in it and fill with hot water so that the glasses are as high as possible in water. Bake for approx. 25 minutes, sprinkle with icing sugar just before serving.

Tip: You could use vanilla pudding powder instead of cornflour.