Dredge meat in flour. In a skillet, melt 1/2 butter over medium heat; saute onions until tender. Remove from pan; set aside. Melt remaining butter and brown meat on all sides. Add broth, basil, salt and pepper, mushrooms, Worcestershire sauce and onions. Cook until mixture thickens, about 5 minutes. Just before serving, stir in sour cream. Heat through, but do not boil. Serve immediately over rice or noodles.