For the crumbles, place the muesli, flour, 150 g sugar, salt and 150 g butter in flakes in a mixing bowl and knead with the dough hooks of the hand mixer. Then work into crumbles with your hands and chill. Beat 125 g butter, 150 g sugar, vanillin sugar and salt with the whisks of the hand mixer until foamy. Stir in the eggs one after the other. Add quark, mascarpone, milk and semolina and stir in. Put half of the crumbles into a greased springform pan (26 cm Ø, with a rim at least 6 cm high). Press down with your hands to a smooth base.
Add the quark mixture by the spoonful and spread the frozen berries between them, smoothing them down. Spread the remaining crumbles on top. Bake in the preheated oven (electric range: 200 °C/ convection oven: 175 °C/ gas: level 3) for 60-70 minutes on the bottom shelf. If the cake gets too dark, cover the surface with aluminium foil. Remove the cake from the oven, place on a grid and carefully remove from the edge. Let the cake cool down for about 5 hours (preferably overnight), then remove from the tin. Dust the edge with icing sugar and serve on a cake plate