Dredge steak strips with flour; reserve remaining flour

Brown strips in melted butter in 12-inch skillet

Add onion and cook 3-4 minutes

Remove meat and onion from skillet

Blend reserved flour into pan drippings in skillet

Cook over medium heat 1 minute, stirring constantly

Stir in beef bouillon and worcestershire.

Stirring constantly, cook until thickened

Stir in salt, mustard, tomato paste

Blend in sour cream

Add mushrooms, cook for about 5-10 minutes until the mushrooms soften

Add meat

Cool quickly

Serve over rice or noodles