Make shortcrust pastry from butter, sugar, egg, flour and baking powder, put in the fridge for a while. Line a cake pan (springform pan, 26 cm diameter) with the shortcrust pastry.
Mix the quark with sugar (if you like it sweeter, you can also use 200 g sugar), eggs, oil, custard powder and vanilla sugar. Add milk as needed. The curd mass should be relatively liquid. Fill on the shortcrust pastry.
Bake the cake at approx. 180 degrees for 1 1/2 hours. Cover with aluminum foil 15 minutes before the end of baking so that the cake does not get too dark.