Heat the oven to 450F.

Let roast stand until it gets to room temperature (about 2hrs). Roast should not be cold in order to cook evenly.

Tie the prime rib before roasting. If left untied, the outer layer of meat will pull away from the rib-eye muscle and overcook. To prevent this problem, tie the roast a both ends, running the cooking twine parallel to the bone. Most butchers will tie your rib roast for you.

Center the roast, fat side up, on a rack in a roasting pan. Sprinkle the garlic cloves around the roast. Combine the horseradish topping and spread it over the surface of the rib roast. Place a meat thermometer in the center, not touching any bone.

Sear the rib roast for 15 minutes at the higher oven temperature (450? F), then turn the oven to the lower temperature (325F) for the rest of the cooking time. Every 1/2 hour, baste the cut ends of the roast with the fat accumulated in the roasting pan.

Roast about 1 3/4 hours, or until the temperature reach JUST under desired doneness which should be 120?. Remove from the oven, cover with aluminum foil, and let it stand for 15-20 minutes. The rib roast will continue to cook as it sets. The temperature will rise to 125F to 130F internal temperature (medium rare) at 15 to 20 minutes. If allowed to rest as long as an hour, the temperature will rise even higher. So, pay attention to how long you let the cooked prime rib roast sit.

Allow additional cooking time for your prime rib roast at high altitude...just watch the meat thermometer.

Optionally: Serve with Wild Mushroom Sauce