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Sear the rib roast (prime rib) for 15 minutes at the higher oven temperature (450 degrees F.), then turn the oven to the lower temperature (325 degrees F.) 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. Do Not Cover the roast.rime Rib Roast (standing rib roast), at room temperature (very important) 2 tablespoons butter, room temperature. Preparation: Preheat oven to 450 degrees F. Pat the room-temperature standing rib roast (prime rib roast) dry with paper towels or napkins.
Prime Rib Cooking Times. These estimated roasting times are based on a minimum roast weight of 4 pounds (or 1.8 kg): Recommended cooking temperature is 325ÂºF. For Medium-Rare: Cook for 22 minutes per pound. Internal temperature on the meat thermometer should read 140ÂºF (or 60ÂºC) when the roast is removed from the oven. For Medium: Cook for 25 minutes per pound. Internal temperature should read 155ÂºF (or 68ÂºC) when roast is removed from the oven.