Prepare fire in charcoal or heat gas grill. Strip corn husks to the stem without removing them; remove silk to expose kernels. Soak corn in cold water at least 10 minutes. While corn is soaking, combine butter, ponzu and garlic. Remove corn from water; wrap husks back over kernels. Grill corn, turning occasionally, 15-20 minutes or until steamed through. Unwrap husks; spread butter mixture on corn and season with salt and cayenne pepper.