1Pat your prime rib dry with paper towel, rub all over with a cut clove of garlic and sprinkle with salt and pepper. Preheat your grill to high.
2Brown your prime rib for a few minutes on each side, until deep golden and char-marked. Transfer it to a cast iron skillet or aluminum roasting pan, and place it on one side of the grill, turning off the heat underneath that side but leaving it on on the other side. Close the lid and cook over indirect heat for about 45-50 minutes - the temperature should be about 400F - until a meat thermometer inserted into the thickest part of the roast (make sure it doesn't touch the bone, which conducts heat more efficiently than the meat itself) reads about 130F for medium-rare.
3Remove from the heat and wrap in foil; let rest for 15-20 minutes before carving. (The temperature will continue to rise as it sits.)