2 tbsp. butter
1 lg. onion, diced
1 can tomato soup
1/2 tsp. dry mustard
2 c. leftover roast beef or London broil, sliced thin and diced
3 oz. jar sliced mushrooms, drained
1 c. sour cream

Melt butter in 3 quart saucepan and saute onion. Stir in remaining ingredients, except sour cream. Heat just to the boiling point, reduce heat and simmer very gently 15 minutes. Stir in sour cream must before serving. Serve over rice or noodles.