Cook noodles according to package directions (omitting salt and fat); then drain and combine with 1/2 cup beef broth in medium cooking pot. Cook ground beef in skillet over medium heat until well-done. Drain and remove from skillet; set aside. Sauté onions and mushrooms in margarine for 3 minutes, or until tender crisp. Sprinkle with flour and season with salt and pepper. Add remaining beef broth and bring mixture to a boil. Simmer for 2 minutes. Add cooked ground beef and slowly stir in sour cream. Return to heat and cook over low heat until warm—do not let boil or sour cream will curdle. Serve over noodles.
