Onions peel, halve and in fine rings separate. Clean and wash the leek and cut into rings. Heat 2 tablespoons of oil in a pan. Sauté the vegetables in it. Season with salt and pepper and let cool off.
Mix the remaining milk and eggs. Season with salt, pepper and nutmeg. Mix quark, milk and 5 tablespoons of oil. Mix flour and baking powder. First stir about 100 g into the quark mixture, then knead in the rest.
Halve the dough and roll out a circle (approx. 20 cm Ø) on a floured work surface. Grease 2 gratin dishes (approx. 18 cm Ø). Place the dough in the moulds and press the rim firmly down.
Prick the bottom several times with a fork. Spread the vegetables on top. Pour egg milk over it. Cut bacon into small pieces and put them on the vegetables. Bake the onion cake in a preheated oven (electric range: 200 ° C/ convection oven: 175 °C/ gas: level 3) for 30-35 minutes.
Remove the onion cake and garnish with parsley.