Dissolve the yeast with the sugar in the lukewarm milk. Put the flour in a bowl and make a well in the middle. Pour the dissolved yeast milk into the well, stir a little and let rise in a warm place for 20 minutes.
Then add the butter and egg and knead everything into a smooth dough. Cover and let rise again in a warm place for 30-60 minutes until the dough has visibly enlarged.
For the cream, mix the quark, cream, egg, cornstarch and sugar and add the hazelnuts, fold in.
Preheat the oven to 180 ° C O / U heat. Grease the baking sheet.
Place the dough on the greased baking sheet, roll it out or spread it out with your hands and pull up a little at the edge. Then put the quark mixture on top and smooth it out.
For the topping, stir together the sour cream, eggs, cornstarch and sugar. Pour on the quark cream, distribute and smooth out. Bake the cake in the preheated oven for about 35 minutes. Let cool down completely and cut into pieces.