Mix flour, 150 g sugar, 1 packet vanilla sugar, cocoa, baking powder and salt in a bowl. Add 150 g butter in small pieces, 1 egg and 3 tbsp. cold water and knead to a smooth shortcrust pastry. Wrap in foil and chill for about 30 minutes.
Melt 400 g butter in a saucepan. Mix quark, 300 g sugar, 1 packet of vanilla sugar, 5 eggs and pudding powder to a smooth cream. Finally, stir in melted butter well.
Lightly dust a large sheet of baking paper with flour. Roll out 600 g dough on the baking parchment to a circle of approx. 38 cm Ø. Line a greased springform pan (26 cm Ø) with the dough and press it to the edge of the pan. Cut off any excess dough evenly all around, up to a 4-5 cm high rim.
Put the curd mixture into the mould and smooth it down. Knead dough sections together with the rest of the dough, pluck into pieces and press flat. Place the dough on the cream and bake in a preheated oven, lowest shelf (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 1 1/4. Cover the cake with parchment paper after 45-60 minutes. Leave the finished cake to rest for 5-10 minutes in a switched-off oven. Then let the cake cool down on a cake rack in the mould. Remove the cake from the tin, lift it onto a cake plate and dust the edge with icing sugar as desired.