Most cooks take advantage of carryover cooking, which simply means removing meat from its original heat source before it reaches the desired internal temperature to let residual heat finish the job. You can apply carryover cooking on a larger scale and cook large cuts of meat, such as boneless prime rib, to medium-rare by using a technique known as "residual-heat roasting." During residual-heat roasting, hot air retained in the oven after an initial sear at 500 degrees Fahrenheit cooks the prime rib to 135 F, or medium-rare. Residual-heat roasting requires less active cooking time than high-temperature roasting, and it cooks the prime rib more evenly, too.
Dry the rib with paper towels 24 hours before you want to cook it. Liberally season the prime rib on all sides -- the fat cap, front, back, sides and bottom -- with kosher salt and massage it in thoroughly.
Set the prime rib in a shallow dish or on a tray. Store the prime in the refrigerator for 24 hours, uncovered.
Take the prime rib out of the refrigerator 2 to 4 hours before you want to cook it. Let it sit out until it reaches room temperature, about 2 to 3 hours for a 2- to 4-pound roast and 3 to 4 hours for a 4- to 8-pound roast.
Heat the oven to 500 degrees Fahrenheit. If you have a convection oven, operate it with the convection fan off.
Set the prime rib on a roasting rack set in a deep roasting pan. Place the prime rib on the middle rack when the oven reaches 500 F.
Roast the prime rib for 5 minutes per pound. For example, if you have a 6-pound boneless prime rib, you need to roast it for 30 minutes at 500 F. Set the oven timer to alert you when to kill the heat.
Turn off the oven. Let the prime rib cook continue to cook using residual heat for 2 hours. Set the timer to alert you when to remove the prime rib.
Take the prime rib out of the oven. Serve the prime rib immediately. You don't have to let the prime rib rest; the residual-heat cooking took care of it.