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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.
4 Place the roast fat side up and rib bones down in a roasting pan. Insert a meat thermometer into the thickest part of the roast, making sure that the thermometer isn't touching a bone. 5 After browning the roast at a 500Â°F temperature in the oven for 15 minutes, reduce the oven temperature to 325Â°F.To figure out the total cooking time, allow about 13-15 minutes per pound for rare and 15-17 minutes per pound for medium rare. prime rib roast is too expensive to wing it. Error on the rare side, you can always put the roast back in the oven to cook it more if it is too rare for your taste. Roast in oven until thermometer registers 115Â°-120Â°F for rare or 125Â°-130Â°F for medium.