Bring a pot of salt water to the boil. Blanch the cabbage leaves for about 2 minutes, rinse with cold water. Peel celeriac and onion and dice coarsely. Melt the fat in a pot. Add celery and 1/3 of the onion cubes. Fry for about 5 minutes, stirring occasionally. Deglaze with 2 tbsp. vegetable stock and cooking cream, bring to the boil, cover and cook for approx. 20 minutes
Cut the thick ribs of the pointed cabbage leaves flat. Wash parsley, shake dry, pluck leaves from the stalks and chop. Season the mince with salt and pepper. Knead with quark, parsley and 1/3 of the onion cubes. Spread the mincing mixture on the cabbage leaves, fold the sides slightly and form a roll
Heat the oil in a frying pan. Fry the pointed cabbage rolls and the remaining onion cubes briefly. Fill up with 5 tablespoons of vegetable stock. Add mustard seeds and caraway seeds, cover and cook over medium heat for about 10 minutes. In the meantime puree celery with a hand blender until creamy, season with salt and pepper
Remove the rolls from the pan. Stir starch with 1 tbsp. cold water until smooth, thicken brew with it, bring to the boil. Put the pointed cabbage rolls and puree on a plate and drizzle the sauce over them