Place this rib roast, with its rib side down on a roasting tray and roast it for about 15-20 minutes. When the meat is nicely seared on the outside with a golden brown color, turn down the heat to around 325º F. After about 1½ hours, insert a meat thermometer to the thickest part of the meat. If it reads 130 degrees, then your roast is done. If the meat thermometer does not register 130 degrees, continue roasting the prime rib at the same oven temperature and check every 10 minutes.