Preheat oven to 450 degrees F.
- Bring the prime rib to room temperature. Pat dry with paper towels and coat the roast with butter, then season with pepper and rosemary. Resist the temptation to salt your prime rib roast. Salt draws out moisture from the meat while cooking.
- Place the roast, ribs down or fat side up, in a heavy stainless-steel roasting pan. Place roast in oven and sear for 15 minutes at 450 degrees F. Reduce the oven temperature to 325 degrees F.
- Peel (most of) the paper off the garlic: Use your fingers to peel away all the loose, papery, outer layers around the head of garlic. Leave the head itself intact with all the cloves connected. Trim about ¼ inch off the top of the head of garlic to expose the tops of the garlic cloves. Drizzle 1 to 2 teaspoons of olive oil over the exposed surface of the garlic, letting the oil sink down into the cloves. Wrap the garlic in aluminum foil and roast in the oven with the rib roast for 40 minutes to one hour. The garlic is done when a center clove is completely soft when pierced with a paring knife.
- Baste the prime rib every 30 minutes. Do Not Cover the roast. About 30 minutes before the estimated end of the roasting time, begin checking the internal temperature. When checking the temperature of your prime rib roast, insert meat thermometer so the tip is in thickest part of beef, not resting in fat or touching bone. Cook until rib roast reaches an internal temperature of 120 degrees F. (or your desired temperature).
- Remove from oven, cover loosely with aluminum foil, and let sit approximately 15 to 20 minutes. Cutting into the prime rib too early will cause a significant loss of juices. Garnish with sprigs or rosemary and serve!