Saute ground beef and onion in butter until meat is browned. Partially drain. Add broth (optional) and Worchestershire sauce. Cover and simmer until beef is tender, stirring occasionally. Add mushrooms with liquid. Combine sour cream and flour; blend into meat mixture. Cook 5 minutes or until sauce is thickened. Meanwhile, cook noodles according to package directions; drain. Serve stroganoff over noodles.