Place the butter in a bowl and stir in the sugar, vanilla sugar and salt. Mix in the egg yolks and continue to stir until the mixture turns paler in colour.
Combine the flour and baking powder, add to the mixture, flatten the dough, cover and refrigerate for approx. 1 hr.
Transfer 2/3 of the dough to the prepared tin, press down evenly, pull the dough upwards to the edge of the tin, cover and refrigerate for approx. 15 mins. Prick the dough base firmly with a fork.
Thoroughly combine the pudding powder and quark, stir in the apples, spread the mixture over the dough base. Crumble the remaining dough by hand, sprinkle the crumble over the top.
for approx. 50 mins. in the bottom half of an oven preheated to 180°C. Remove from the oven, allow to cool on a cooling rack. Remove the cake from the tin, dust with icing sugar.