A large prime rib roast is one of the most dramatic entrees for a lavish meal, with its massive bones and big "eye" of tender, well-marbled beef. At a good restaurant, it's served in thick slices that remain beautifully pink and tender from the center all the way to the edge. Producing a restaurant-quality roast at home requires no special equipment, just good basic technique.
Making the Grade
Some of the tenderest cuts of beef come from a long group of muscles that run from the animal's shoulder all the way to the sirloin. Prime rib or standing rib roast come from the portion that lines the first seven ribs, where it's tenderest and has the most marbling. A full standing rib is a huge roast, so they're often sold in smaller portions containing two to four ribs. For a restaurant-quality result, buy the best beef you can find. Prime grade is rare and costly, and Choice is less marbled but can still be memorable. Select is the least expensive and is still a good roast, though not comparable to the higher grades. Best of all is dry-aged Prime beef, though it's difficult to find and commands a premium price.
You can cook a good-quality prime rib without any preparation and still have an excellent roast, but it takes only a little more work to make it memorable. Start by seasoning the meat over all its exposed surfaces, either with salt and pepper or more potent flavorings such as good mustard, minced garlic or fresh herbs. You can even cut away the ribs, season the roast on all sides, then tie the ribs back on, if you wish. Use a paring knife or a noose of dental floss to scrape the tips of the bones as clean as possible, which does little for the roast's flavor but makes its appearance neater and more professional.
Rather than cooking your roast at 325 or 350 degrees Fahrenheit, as most cookbooks recommend, heat your oven to 225 F. Ordinary high-temperature roasting produces a finished prime rib with a band of well-done beef around the outer edges, and juicier medium-rare beef inside. By slow-roasting your prime rib at low temperature -- it can take three to four hours, depending on the size of your roast -- you'll get a perfect medium-rare across the entire slice. A big prime rib will continue to cook after you take it out of the oven, so for a final medium-rare temperature of 130 F you need to take it when it reads 120 F on your instant-read thermometer. Note that the U.S. Department of Agriculture recommends all beef cuts be cooked to an internal temperature of 145 F.
The Finishing Touches
Low-temperature roasting produces a perfectly moist and tender piece of prime rib, but it can't generate the dark, savory crust you get from high heat cooking. It's best to do that at the end, by removing your roast from the oven for several minutes and cranking its heat to 500 F. Put the roast back in for eight to 10 minutes, until it's darkly browned, then take it out and let it rest under a loose covering of foil. It's best after resting for at least 15 to 20 minutes. For easy carving, cut the whole roast away from the bones and slice it. Separate the rib bones and leave them on the serving tray for those who like to gnaw them.