Cut meat across the grain into 3/4-inch slices, then into strips 3x1/4 inch. Melt 1/4 cup butter in a large skiller. Cook and stir mushrooms in butter about 5 minutes, remove mushrooms. In same skillet, brown meat. Reserving 2/3 cup of broth, stir in remaining broth, the onion, catsup and garlic salt. Cover and simmer 15 minutes. Blend reserved broth and the flour; stir into meat. Add mushrooms; heat to boiling, stirring constantly. Boil and stir 1 minute. Stir in sour cream, heat through. Cook noodles as directed on package; drain. Toss with 3 tbs. Butter. Serve with stroganoff.