Peel the onions, cut off a small lid and hollow them out with a spoon until the edge is about 1/2 cm wide. Cover and cook onions in boiling salted water for 15-20 minutes.
Bring 1/4 litre of vegetable stock to the boil. Sprinkle with buckwheat groats and let it swell for about 5 minutes at low heat. Leave to swell for a further 10 minutes with the hotplate switched off. Finely chop onion cap and onion interior.
Peel, wash and thinly slice the carrots. Melt the fat. Fry diced onions until translucent and add half to the buckwheat groats. Add the carrots to the remaining onions and fry briefly.
Deglaze with remaining vegetable stock, bring to the boil, cover and cook for about 15 minutes. Wash and chop the parsley and add half of it with the egg and quark to the buckwheat. Season with salt, pepper and coriander.
Pour the mixture into the drained onions. Puree the carrots. Add remaining parsley to the sauce. Season sauce with salt and pepper and pour into an ovenproof dish. Add the onions to the sauce. Cook in the preheated oven (electric cooker: 175 °C/ gas: level 2) for approx. 25 minutes.