Peel and wash the potatoes and cook in salted water for about 20 minutes
Peel the carrot, clean the leek, wash both and cut into fine strips. Clean, wash and quarter the mushrooms. Wash the meat and pat dry
Fry the mushrooms in hot oil until golden brown. Season and remove. Deglaze frying fat with 1/8 l water, bring to the boil, stir in broth. Steam covered fillet for about 10 minutes. Cook vegetables and mushrooms for 2-3 minutes
Remove the fillet and vegetables. Keep warm. Stir horseradish into the stock, bring to the boil and thicken. Stir in cream. Season to taste. Drain potatoes. Serve with meat, vegetables and sauce. Sprinkle with chives
If you do not want to buy extra sour cream, you can also refine the sauce with some milk instead