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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. full rack of prime beef is 7 ribs, which will easily serve 14 to 16 people. A full rack will not fit in my oven, so when Iâm feeding a crowd, I cut the roast in half (3 ribs on one roast and 4 ribs on the other) and cook them in separate ovens.