Reheating a boneless prime rib takes patience if you want to prevent it from drying out. You can reheat a prime rib using any heat source, but for safety and the best outcome, use an oven or microwave. However you decide to reheat your prime rib, don't rush it or use high heat for long periods.
Remove the prime rib from the refrigerator and let it reach room temperature. This will ensure the meat reheats evenly. If you put cold meat in the oven or in the microwave, the exterior will cook faster than the interior.
Preheat an oven to 200 to 350 degrees depending on if you want your meat more rare or well done. The temperature will depend on how much meat you are reheating and your desired internal temperature.
Thick slice vegetables such as carrots, celery, potatoes, green peppers or onions if you wish to cook them with the prime rib.
In the Oven
Place the meat on a rack inside a roasting pan if you want to let excess fat drip away. Place it directly in a roasting pan if you don't mind the excess fat. Place the meat on top of vegetables if you want the excess dripping to coat the vegetables.
Place the roasting pan on the center rack of the oven and let the meat cook for 15 minutes if you want a rare prime rib. Cook for 30 minutes for medium, and 45 minutes for well. Use a higher temperature for cooking a rare or medium rare prime rib, since you will be cooking it less. Use a lower temperature if you plan to cook the prime rib long enough to let it reach medium well or well done temperature.
Remove the prime rib from the oven and let stand for a minimum of five minutes. Letting it rest will allow the internal liquid to reabsorb back into the meat. If you cut the meat immediately after removing it from the oven, you will let the juices that have bubbled to the surface run out into the pan or onto the plate or cutting board.
In the Microwave
Find the reheat or warming setting on your microwave. Some microwaves may ask for a desired cooking time after you select reheat, while others may ask for the weight of the meat.
Place the prime rib into the microwave on a non-metal plate. Insert a cooking probe into the meat if the microwave comes with one. Follow the directions on the probe. Some may give a temperature reading, while others offer a "doneness" setting. Cook to an internal temperature of 120 degrees Fahrenheit for rare, raising the temperature if you want the meat more well done.
Close the door on the microwave and turn it on. Monitor its progress every five minutes or so. A microwave can overcook a piece of meat if you heat it even one minute too long.
Things You'll Need
Microwave temperature sensor
Your favorite vegetables