Brown beef, season to taste, in melted margarine until loose and crumbly. Lift meat out of pan.
Add mushrooms and onion. Cook over low heat until onion is soft and transparent. Remove from pan.
Add flour to pan, stirring to make a smooth pasted (If you need to add butter so there is 2Tbsp before you add the flour)
Blend in beef broth, stirring over medium heat until thickened and bubbly.
Return meat and mushroom mixture to pan. Stir in sour cream.. Cook until heated through. Do not let boil or sour cream will curdle.
Serve at once over hot noodles or rice.