Select the berries, wash and drain well. Coarsely chop the pistachios. Knead butter, 200 g flour, 50 g sugar, pistachios and vanillin sugar with the dough hooks of the hand mixer or with your hands to crumbles. Put them in a cold place
Mix berries, lemon juice and jam sugar in a pot and let it stand for about 15 minutes. Mix quark, milk, oil, 75 g sugar and salt. Mix 450 g flour and baking powder and stir about half into the quark mixture. Knead in the rest of the flour. Wrap the dough in foil and chill for about 1 hour
Bring the berries to the boil while stirring occasionally and let them simmer for 2-3 minutes. Remove the pot from the heat and let it cool down while stirring occasionally
Roll out the dough to a rectangle (approx. 32 x 39 cm) on a floured work surface and place on a greased baking tray (32 x 39 cm). First spread blueberry jam, then the crumbles on the dough. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for about 20 minutes. Let the cake cool down and cut into pieces. Whipped cream tastes good with it
Waiting time approx. 50 minutes