Clean the leek, wash it and cut it into rings. Peel onions, slice or cut into fine rings. Heat 1 tablespoon of oil in a large coated pan. Fry the leek in it. Add onions, fry until transparent. Fry ham and marjoram briefly. Season with salt and pepper, let cool off
Mix 225 g flour and baking powder. Add the quark, milk, 5 tablespoons of oil and 1 pinch of salt and knead until smooth. Roll out the quark and oil dough on a little flour to a rectangle (approx. 26 x 34 cm). Line a thinly greased ovenproof dish (approx. 22 x 30 cm; approx. 2 l capacity) with the dough and press down at the edges. Prick the base several times
Spread the onion mixture on the dough. Mix the soured milk and eggs, season and pour over the mixture. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/gas: level 3) for approx. 35 minutes until golden brown. Garnish and possibly serve with a dollop of soured milk