Using the whisk on a hand mixer, beat the butter, sugar and salt in a bowl. Add the eggs and continue to beat until the mixture becomes lighter in colour. Mix the flour, cocoa powder and baking powder, stir into the egg mixture. Cover the dough and chill for approx. 30 mins.
Roll out one third of the dough on the baking paper on the tin base, close the tin frame. Shape one third of the dough into a roll approx. 70 cm long, place around the edge of the pastry base, press gently and pull upwards to the edge of the tin. Prick the dough base firmly with a fork, chill.
Using the whisk on a hand mixer, beat the butter, sugar and vanilla sugar in a bowl. Add the eggs one at a time and continue to whisk until the mixture becomes lighter in colour. Stir in the quark. Spread the mixture over the dough, tear apart the remainder of the chocolate dough, scatter over the top.
Approx. 70 mins. in the lower half of an oven preheated to 180°C. Switch off the oven and leave the cake to cool for approx. 15 mins. with the oven door open. Remove from the oven, carefully remove the tin frame, slide the cake onto a rack and leave to cool.