Preheat grill. Cut butter into (8) 1/4-wide slivers 1-inch long. Make 8 1/2-inch slits in top skin and slip butter into slits. Push any extra butter into the folds created when the breast is wrapped. Salt and pepper over all. Cook for 5 minutes at high heat, then to medium heat. Grill until the internal temperature reaches 175°F.   Remove and let cool 20 minutes before carving. If you need drippings for gravy, set a drip pan on bars or bricks under the rack, and remove it after the first 30 minutes (or else it will burn off).