Older cookbooks will sometimes instruct you to remove excess fat from the roast. “Excess” fat is any fat more than an inch thick on the roast. Fat is what you need to give the roast flavor and to make it juicy and tender. Prime rib is expensive and you are paying good money for that fat so leave it on. Your butcher should have removed any excess fat.
The most important piece of advice I can give you regarding cooking a prime rib roast is to use a good meat thermometer! I recommend this ChefAlarm by ThermoWorks. With a remote thermometer you can tell exactly what the temperature of the meat is without having to open the oven door.
- One standing rib roast, 3 to 7 ribs (estimate serving 2-3 people per rib), bones cut away from the roast and tied back to the roast with kitchen string (ask your butcher to prepare the roast this way)
- Freshly ground black pepper
- Digital thermometer
- Large roasting pan