Peel and wash the potatoes and cook them in boiling salted water for about 20 minutes. Boil eggs in boiling water for 8-10 minutes until hard. Wash herbs, dab dry, put 4 stalks of Pimpernelle aside for garnishing.
Finely chop the rest. Onions peel and in fine cubes cut. Drain eggs, quench and peel. Take out the yolk from 2 eggs and pass through a sieve. Chop the egg white finely. Put herbs, except 1 tablespoon for garnishing, onions, egg yolk and egg white in a bowl.
Add vinegar, oil, sour cream and yoghurt to the herbs. Season with salt, pepper and sugar. Drain the potatoes and rinse briefly. Halve the remaining eggs. Serve with sauce and potatoes on preheated plates.
Garnish with 1 stalk of pimpernel and chopped herbs.