Preparation / Directions:
Cut beef into narrow strips about 2 1/2" long. Dust the strips with salt and pepper. Melt 2 T. of the butter and saute the mushrooms. Set aside. In same butter saute the peeled and sliced onion until brown and set aside. Add rest of the butter to pan and saute the beef. Add the flour, browning well. Slowly add the broth, sherry, tomato paste and the mustard. Blend well. Let simmer for about 20 minutes. About 5 minutes before serving, add the sour cream and blend thoroughly.