Preheat the oven to 180 degrees circulating air. Butter four small portion molds well and then sprinkle with the sugar. Separate the eggs and beat the egg whites with a pinch of salt until stiff. Mix the egg yolks with the powdered sugar, vanilla sugar and cornstarch until frothy. Add the quark and stir the mixture until smooth. Then carefully fold in the egg whites. Pour the mixture into the molds and bake in the preheated oven for about 18-20 minutes.