Grab a shallow pan and place the prime rib in it with the bone side facing down. Roast it at 450 degrees F for 15 minutes to sear the outside, and then turn the oven down to 350 degrees F. Continue roasting the prime rib for 45 to 90 minutes, depending on how done you like your meat. Check it by inserting an instant-read thermometer in the meatiest part of the roast.