2 lbs. lean sirloin or bottom round (in 1 piece), trimmed
2 tsp. salt
1/2 tsp. pepper
4 tbsp. butter
1 med. onion, thinly sliced
1 tbsp. flour
1 tsp. mustard powder (or 1 tbsp. prepared dijon)
1/2 c. dry white wine
2 tsp. tomato paste (optional)
1 tbsp. minced onion
1/2 lb. mushrooms, thinly sliced
2 tbsp. dry white wine
1 c. sour cream, warmed

Cut meat into 1/2 inch slices. Place between 2 sheets of waxed paper and pound with mallet until meat is 1/4 inch thick. Cut meat into 2 x 1/2 inch slices and place on large platter. Sprinkle with salt and pepper; let stand at room temperature for 15 minutes. Heat 2 tablespoons butter in a deep, heavy fry pan or saucepan, enough to hold all ingredients. Add onion (sliced) and cook until soften. Add meat and cook for 3 minutes, browning all sides. Stir in flour and mustard; stir and cook for another minute. Add the 1/2 cup wine and optional tomato paste. Reduce heat to low, cover pan, and simmer for 10 minutes, stirring frequently. In another frying pan, heat the remaining butter; add minced onion and mushrooms; cook for 2 minutes. Add 2 tablespoons of wine and cook 2 minutes - mushrooms should still be firm. Add mushrooms to the meat; check seasoning and stir in sour cream. Over low heat, simmer for 5 minutes more. DO NOT BOIL. Serve over a bed of rice or noodles. Serves 4 to 6.