Make a shortcrust pastry with the flour, butter, 50g sugar and egg yolk and put it in the fridge for an hour. Line a greased springform pan with it and bake in a preheated oven at 175° for 15-20min. Let cool and then place the cake base on a cake plate and enclose with the springform pan rim or cake ring.
Separate the eggs. Separately, beat egg whites and cream until stiff. Beat egg yolks, remaining sugar and vanilla sugar until foamy.
Add quark. Soak gelatine according to instructions, squeeze out and dissolve over low heat. Carefully fold into the quark mixture. Then fold in the egg whites and cream one after the other. Clean the strawberries, cut in half if necessary and spread on the short pastry base.
Keep some for decoration. Spoon the quark mixture over the strawberries and carefully smooth it down. Leave the cake to set in the refrigerator for 3-4 hours. Decorate with the remaining strawberries.