The meat is cut into 5 cm long, 2 cm wide strips. Chop the onion thinly, mushrooms without stumps, also cut into thin. Low heat in a pan melt half of the butter and add the onions. Stir regularly until soft and made transparent. It is important not to burn. Add the mushrooms and stir for about a minute until soft and absorb the sauce. Onions and mushrooms in separate bowl. Add the remaining butter to the pan and heat until begins to foam. Add the meat into strips and fry on all sides - the meat should only be fried outside, but inside is not too well cooked. Add onions and mushrooms back in the pan, season with salt and pepper, add the cream and leave the same temperature of the fire for about a minute so that the cream sauce becomes thick. Serve warm.