In large fry pan cook steak, mushrooms, onions in hot oil till golden brown

Add boullion, water, salt, tomato paste and mustard

Cover and simmer 30 minutes or until tender

Combine flour and water

Stir into meat mixture

Cook stirring, constantly until mixture comes to boil.

Reduce heat and stir in sour cream

Heat but do not boil

Serve over rice or noodles