Remove husks and silk from corn. Place each ear on a double thickness of heavy-duty foil (about 18x12 in.). Add 1 tablespoon butter and 1 ice cube. Wrap securely, twisting ends of foil to make handles for turning.
Grill corn, covered, turning occasionally, over medium direct heat until tender, about 25 minutes. Open carefully to allow steam to escape. Sprinkle with salt and pepper; if desired, serve with additional butter.