Sauté onion, green pepper, and garlic in butter in a large skillet until tender. Add flour, chili powder, and salt; stir until smooth. Cook 1 minute, stirring constantly. Add tomato and beef broth; cook over medium heat, stirring constantly, until thickened and bubbly. Stir in hot sauce, if desired. Serve sauce hot with roast beef, steaks, meat loaf, or cold meats.