If frozen blueberries are used, defrost them first. Sort fresh berries, rinse in a sieve and pat dry carefully.
Cut the cold butter into pieces, quickly knead with the flour and 1 egg to form a dough. Wrap the dough in cling film and refrigerate for 30 minutes.
Preheat the oven to 200 ° C. Meanwhile, mix the quark, the remaining eggs, sugar and vanilla sugar into a cream.
Roll out the dough on a well-floured work surface. Line the bottom and edge of a tart pan (30 cm) with it. Pour in the quark mixture and top with the blueberries.
Bake the cake in the oven at 200 ° C for about 30 minutes. Garnish with mint and powdered sugar before serving.