Perfect Prime Rib Roast

Makes 6 to 8 servings

There are several grades of meat, in order: Prime, Choice and Select, and then there is the Grass Fed. The one I cooked is Choice but I would have preferred to select the Prime Grade. If you are cooking for people who do not like rare or medium-rare and they like their meat more well-cooked,  then the advice is to buy a cheaper cut of meat like Select.
The ideal standing rib roast should contain 3 - 5 ribs, and we think 3 is the perfect size for dinner for 6-8. For more guests (or more leftovers), order a 4 or 5-rib roast. Either way, ask fro a small end(or first-cut) roast, meaning a roast cut from the loin end of the steer, where the meat is tender, flavorful and leaner than at the large end.
Note that the roasts we bought for the FOODday Test Kitchen were sold with the bones cut off the meat and then tied back on. If your roast has not been prepared in this manner, ask the butcher to cut and tie it for you.  (MJ-I did not bother with all this, just found a Choice 3 rib roast at Costco and that cost was about $40.99, the label on the package: Beef Rib Roast Bone In Standing Rib USDA Choice)
1    3-bone beef rib roast (prime rib), about 6 pounds
2     tablespoons kosher salt
1     tablespoon freshly ground black pepper
1     teaspoon dry mustard
2     teaspoons chopped fresh rosemary
6     to 8 sprigs fresh rosemary (optional)
Creamy Horseradish Sauce:
1/4 cup prepared horseradish sauce
1 cup sour cream
2 teaspoons Dijon mustard (optional)
1/4 cup finely chopped green onions or fresh chives
At least one day ahead of time, unwrap roast and pat dry with paper towels.
Combine salt, pepper, dry mustard and chopped rosemary;
rub generously all over roast, especially in spaces between meat and bones.
Refrigerate, uncovered.
Up to two hours before cooking the roast, remove from refrigerator and let sit at room temperature, loosely covered.
Position a rack in the center of oven and preheat to 450 degrees. (For grass-fed beef, start at 350 degrees).
Place roast bone side down in a large, shallow roasting pan on a bed of rosemary sprigs, if using (for boneless roasts, line the pan with a roasting rack).
Place meat in the oven and roast for 20 minutes, then, without opening the door, reduce oven temperature to 350 degrees. After about 45 minutes, start checking the internal temperature of the roast with an instant read, probe or continuous-read meat thermometer.
Remove the roast at 115 degrees for rare (1 to 1 1/2 hours), 120 to 125 degrees for medium rare, and 130 for medium. Tent with foil and let roast sit for 15 to 30 minutes;
as it rests, the juices will be redistributed in the meat and the internal temperature will rise by about 10 degrees.
Carve the roast at the table and serve. Serve with Creamy Horseradish Sauce.

To make sauce:
In a medium bowl stir together horseradish sauce, sour cream, Dijon mustard, if desired, and green onions or chives.

When using a convection oven, resting temperature of roast can rise as much as 30 degrees, so remove roast at 110 degrees for rare, 115 to 120 degrees for medium rare and 125 for medium doneness.

Oregonian FOODday, Dec. 18, 2007