Peel and dice potatoes. Pell onion, chop finely and sautée in oil. Add potatoe cubes and pour over beef stock after some minutes. Let all simmer for about 15 minutes.
Spice fish filets and fry them on both sides about 4 minutes.
Dice gherkins. Chop 1 tbps. dill finely. Add gherkins, dill and creme fraiche to the potatoes and mix carefully. Season to taste and serve with fish filets.