Broiling Directions: Heat broiler. Brush butter mixture over mushrooms, onion and cut-sides of buns. Place mushrooms and onions on broiler pan. Broil 6 to 8 inches from heat, turning once and brushing with remaining butter mixture, until mushrooms are tender (6 to 8 minutes). Place buns on broiler pan, cut-side up. Broil 6 to 8 inches from heat until toasted (1 to 2 minutes).