Cut the loin into slices about 1.5 cm thick and beat into thin layers. Add salt and pepper on both sides. Mushrooms are cut into slices. Peel and onion and chop finely. Melt half of the butter in a frying pan and fry the onion until golden brown. Add mushrooms. Cook, stirring, for 5 minutes. Add salt and pepper.

Put a little stuffing on each layer of meat, sprinkle with grated cheese and roll. Pierce them with a toothpick and tie them with cooking twine. In the same pan, fry the rolls until golden brown. Pour in the broth, if there is any mushroom filling left, also add. Bring to a boil, cover and simmer on low heat for 30 minutes.

Mix sour cream with flour and add to the sauce for krucheniki, salt and pepper to taste. Simmer until the sauce thickens for another 10 minutes. Remove toothpicks and cooking twine, serve croutons in a sauce with buckwheat, mashed potatoes or pasta.