Mix flour and baking powder. Add quark, milk, 3 tablespoons of oil and 1/2 teaspoon of salt and knead to a smooth dough. Peel onions and cut into rings. Heat 1 tablespoon of oil in a pan. Leave out the bacon.
Add onions and stew for about 5 minutes. Season with salt, pepper and marjoram. Roll out the dough on a lightly floured work surface until round (30 cm Ø). Place in a lightly greased quiche tin (26 cm Ø) and press the rim up slightly. Add onions and bacon. Grate the cheese. Whisk eggs and sour cream. Stir in half the cheese. Season with salt and pepper and pour over the onions. Sprinkle the rest of the cheese on top.
Grate the cheese. Whisk eggs and sour cream. Stir in half the cheese. Season with salt and pepper and pour over the onions. Sprinkle the rest of the cheese on top. Cook in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 30 minutes. Arrange the quiche on a plate and serve garnished with marjoram