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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.
Your cooking times will vary depending on the size of your prime rib roast. To calculate your cooking time, multiply the exact weight of the roast by 5. Round the resulting number to the nearest whole number. The rib is cooked at 500 degrees F for exactly that many minutes. For example, for a 6 pound roast: 6x5=30, so cooking time is 30 minutes. Turn the oven off and wait 2 hours before opening the oven door. Remove the prime rib and slice into the most perfectly medium-rare meat you've ever seen.