Warm the milk lukewarm. Mix yeast and 50 ml warm milk. Put 250 g flour and 50 g sugar in a bowl and make a depression in the middle. Pour in the yeast milk and mix with some flour from the rim. Cover and leave to rise for about 15 minutes.
Coarsely chop the walnuts. Knead 100 ml milk and 50 g butter into the pre-dough, cover and let rest for about 30 minutes. Put 100 g flour, 30 g sugar, vanillin sugar, 50 g butter, salt, walnuts and egg yolk into a bowl and work into crumbles first with the dough hooks of the hand mixer, then with floured hands. Put the crumbles in a cool place. Wash the grapes and pluck them from the stems. Form grape-sized balls from the marzipan. Roll out the yeast dough on a floured work surface and place it in a greased springform pan (26 cm Ø). Press the dough to the edge and let it rise again for about 10 minutes. In the meantime mix sour cream, quark, 75 g sugar and eggs. Stir in sauce powder.
Roll out the yeast dough on a floured work surface and place it in a greased springform pan (26 cm Ø). Press the dough to the edge and let it rise again for about 10 minutes. In the meantime mix sour cream, quark, 75 g sugar and eggs. Stir in sauce powder. Spread the grapes and marzipan on the base, pour the sourdough on top and sprinkle with the crumbles. Bake the cake in the middle of the preheated oven (electric oven: 200 °C/ convection oven: 175 °C/ gas: level 3) for 25-35 minutes. Serve the cake lukewarm or cold
Waiting time approx. 50 minutes