Sieve 250 g flour onto the work surface, make a depression in the middle, add egg yolk and sour cream. Spread 125 g fat and half of the lemon peel on the edge of the flour and knead into a smooth dough.
Let the dough rest in a cool place for about 1 hour. Roll out 2/3 of the dough on a greased baking tray to form a rectangle (32x18 cm), border with a collapsible aluminium frame and bake in the preheated oven (electric oven: 175°C/ gas: level 2) for 15-20 minutes.
In the meantime, beat the quark, sugar and vanillin sugar until foamy, gradually adding 3 eggs and the remaining lemon peel. Melt the remaining fat. Stir the melted fat and milk powder into the quark mixture, sieve the remaining flour on top and fold in.
Pour the curd mixture onto the pre-baked base and smooth it down. Roll out the rest of the dough on a floured work surface, cut into strips with a dough wheel and place them on the quark mixture to form a grid and bake in a preheated oven (electric: 175°C / gas: level 2) for 45-50 minutes.
Whisk the rest of the egg and brush the grid with it halfway through the baking time. Results in about 14 pieces.