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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.
Cooking Prime Rib. The U.S. Department of Agriculture safe food handling guidelines recommend heating meat to a minimum interior temperature of 145 degrees Fahrenheit. To achieve this with prime rib, allow about 10 to 20 minutes per pound, depending on the size of the roast and the desired level of doneness. Begin by searing the roast at 450 degrees for 15 minutes, then continue cooking at 325 degrees until the meat thermometer registers the desired temperature. Smaller roasts cook faster while thicker roasts take longer. For a rare roast, cook to 120 to 125 degrees. For medium rare, cook to 130 to 135 degrees.