In a large skillet, melt butter or margarine. Stir in cooking oil. Trim any separable fat from steaks. Add steaks to skillet and cook over medium to medium-high heat for 10 to 12 minutes or to desired doneness, turning once. Transfer to a serving platter, reserving drippings in skillet. Keep steaks warm.
Stir mushrooms, green onions, rosemary, garlic, and pepper into reserved drippings. Cook and stir over medium-high heat for 3 to 4 minutes or till mushrooms are tender. Reduce heat. Carefully stir in sherry, wine, or beef broth. Cook and stir about 1 minute more or till heated through. Spoon over steaks.