Cream butter, 175 g sugar, salt and 1 packet of vanilla sugar with the whisks of the hand mixer. Stir in the eggs one by one. Mix 250 g flour and baking powder and stir into the butter cream alternately with the milk.
Fill half of the dough into a greased springform pan (26 cm Ø), dust with flour. Sort the blackberries, wash, dab dry and puree 75 g. Stir the puree with 2 tbsp. flour into the second half of the dough and spread on the other half.
Swirl a little with a fork and smooth it down. Spread 175 g blackberries on top and bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 35 minutes.
Remove and let it cool down.
Soak gelatine in cold water. Crumble cookies in a freezer bag with the help of a dough roll. Whip the cream with the whisk of the hand mixer until stiff. Remove 50 g cream and chill.
Mix quark, 1 packet of vanilla sugar, lemon juice and 75 g sugar. Squeeze out the gelatine, dissolve and stir in 4 tbsp. of the quark, stir into the remaining quark. Gradually fold in the cream. Fold in cookie crumbs.
Remove the base from the springform pan, place on a cake plate and enclose with a cake ring. Spread the quark cream on top and refrigerate for at least 2 hours. Carefully remove the cake from the ring and spread the edge with the remaining cream.
Coarsely crush 100 g blackberries with a fork and place them in the middle of the cake.