Peel, wash and slice the potatoes. Heat 2 tablespoons of oil in a pan. Fry the potatoes at medium heat for about 20 minutes. Season with salt and pepper. Clean, clean and slice the mushrooms.
Peel and halve the shallots. Dab meat dry and cut into strips. Heat 2 tablespoons of oil in a pan. Fry the meat in it in portions for about 4 minutes. Season with salt and pepper and remove.
Add shallots and mushrooms to the frying fat and fry. Add meat and dust with flour. Add stock, bring to the boil and simmer for about 3 minutes. Cut cucumbers, except 4 for garnishing, into slices and add to the meat.
Refine with mustard and cream, season again. Cut the remaining gherkins in a fan shape. Arrange roast potatoes and Boeuf Stroganoff on plates, garnish with gherkin fans.