In a skillet, heat oil and 2 tablespoons of butter over medium-high heat. Cook steaks for 6-7 minutes on each side or until meat is done as desired (for medium-rare, a meat thermometer should read 145°; medium, 160°; well-done, 170°). Remove to a serving platter and keep warm. To pan juices, add mushrooms, onions and remaining butter; saute until tender. Add flour, salt and pepper; gradually stir in broth until smooth. Add browning sauce if desired. Bring to a boil; boil and stir for 2 minutes. Spoon over the steaks. Serve immediately.