Cut the beef fillets into strips. Finely dice the onion, cut the pickles and mushrooms into slices.
Fry the beef strips in a little oil and remove from the pan.
Now briefly fry the onion with the mushrooms and sprinkle with two tablespoons of flour.
Deglaze with the soup and bring to the boil. Stir in mustard and sour cream. Add meat and pickles, bring to the boil again briefly.
Season to taste with salt, sugar and pepper.