200 g of beef (tenderloin); 1 tbsp.of sour cream; 1 tbsp. of powder of dried mushrooms (optional); 1 onion; 4 tbsp. of ghee butter or lard; 1 tsp. of mustard; 1 tbsp. of flour; salt, black pepper
Sauté finely chopped onion over medium heat until tender in half of the oil, add the mushroom powder, mix well. Add the sour cream, mustard, salt, pepper, warm, remove from heat, and cover with lid. Clean the meat off the sinews, cut crosswise into thin slices, then into strips. Dust in flour, then fry in the remaining oil over high heat until light brown; add the sour cream sauce, warm, let stand, covered for 10 minutes. Serve with crispy potato strips, wide noodles or buckwheat kasha.