Rinse the beef thoroughly and dry it with a paper towel. Cut into medium-thick pieces, then beat.
Heat a frying pan with half the butter over high heat, add the meat, distributing it throughout the pan, and fry until lightly browned, about 15 minutes.
While the meat is cooking, wash and peel the oyster mushrooms. Cut into strips. Heat a second frying pan with the remaining butter, cut the onion into thin half rings and fry over medium heat until the onion is soft and translucent.
Pour 2 tbsp into a saucepan. l. flour and put on fire. Slowly pour sour cream into the flour, add salt and pepper and mix with a spatula until smooth. Add the fried onion to the sauce and keep it on the fire a little longer. The sauce is ready.
Add mushrooms to the meat and fry for about 5 minutes. Then pour in the sauce, salt and pepper. Next, cover with a lid and simmer for about 20 minutes.
Serve in individual portions with fresh vegetables. Garnish with basil and young onions.