Wash potatoes thoroughly and cook in boiling water for about 20 minutes. Boil egg in boiling water for about 10 minutes until hard, rinse and peel. Wash herbs, shake dry and chop coarsely.
Set something aside for garnishing. Cut the cress from the bed and mix with the herbs, except for a little for garnishing.
Mix herbs with curd and milk. Season to taste with salt, pepper and sugar. Finely chop the egg and stir into the sauce. Drain potatoes, arrange with quark and sprinkle with cress and herbs.