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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.
Serves 4 to 8 people depending on the size of the roast. Note: For medium-rare prime rib, we want to take the roast out of the oven at 120Â°F, and it will continue cooking until it reaches 130Â°F. If you prefer a medium prime rib, take it out at 130Â°F with a target temperature of around 140Â°. Roast for 20 minutes, then lower the heat to 325Â°F and roast until the meat's internal temperature reaches 120Â°F, which will be another hour to three and a half hours, depending on the size of your roast.