Add all-purpose and semi-coarse flour to a bowl, add the baking powder packet, powdered sugar, and lemon zest. Mix together, then form a well in the centre, into which you will crack two Dr. Eggs, softened butter, and form a dough. Let the dough rest in a cool place for half an hour.
Grease a 30 x 40 cm pan with butter and coat with semi-coarse flour.
Remove the dough from the refrigerator, and divide into two unequal parts. Place the larger one on a pastry board and put the smaller one back into the refrigerator. Roll out the dough on the pastry board to the same size as the pan, or divide into three parts and roll separately so that the dough covers the entire area of the pan. Don’t forget about the edges of the cake (the dough should go up the sides of the pan as well), and press in with your hands.
Pre-heat the oven to 175 degrees Celsius.
Separate the yolks and whites, and beat the whites until stiff. In a bowl, mix the yolks with the quark, packet of vanilla sugar, and you can also sweeten with powdered sugar to taste (if the mixture is too thick, you can thin with some milk). Then carefully fold in the egg whites. Spread the quark and egg white mixture onto the dough.
Remove the remaining dough from the refrigerator and divide into two parts. Roll the first part out thinly on a floured pastry board. Using a cookie cutter (or knife) cut into strips, approx. 1 cm wide, and lay diagonally onto the quark mixture. Do the same with the second part, but lay the strips in the opposite direction, creating a lattice on the cake.
Bake in a pre-heated oven for approx. 40 minutes. Every oven bakes a little differently, so the baking time is approximate. The cake must be baked until golden.
Don’t slice the cake until properly cooled.