Here’s an easy, virtually foolproof method for cooking perfect, crusty on the outside, meltingly tender inside prime ribs every time. Keep in mind that the only remotely challenging aspect to cooking prime ribs is timing, and if you figure on 12 to 14 minutes per pound (for a bone-in roast), you’ll make a perfect roast every time. Besides, you can let a cooked prime-rib roast stand for up to 30 minutes before carving. Indeed, at least 10 to 15 minutes of standing time is recommended to allow the juices to flow from the center of the roast back to the exterior.
Step 1: Prepare the beef: Using the tip of a slender paring knife, make a series of 1/2-inch-deep holes in the roast, mostly in the sheath of fat on top, but also in the sides and bottom. The holes should be about 2 inches apart. Insert slivers of garlic in half of the holes. Strip the leaves off one or two of the rosemary sprigs and insert them in the remaining holes (or insert the dried rosemary). Slide the remaining sprigs of rosemary under the string used to tie up the roast.
Step 2: Make the rub: Grind the peppercorns and dried rosemary to a fine powder in a spice mill or blender. Add the salt and paprika and grind to mix. Rub the mixture all over the roast, especially over the sheath of fat on top.
Step 3: Set up the grill for indirect grilling, place a large drip pan in the center, and preheat the grill to medium.
Step 4: When ready to cook, brush and oil the grill grate. Place the roast, fat side up, on the hot grate over the drip pan and cover the grill.
Step 5: Grill the roast until cooked to taste, 3 1/2 to 4 hours for a medium-rate roast of this size, figuring on 12 to 14 minutes per pound. (If using a charcoal grill, you’ll need to add 10 to 12 fresh coals to each side every hour. If using a gas grill, keep the cover closed at all times.) Use an instant-read meat thermometer to test for doneness; you’ll want to cook the roast to 145 degrees F for medium-rare, 160 degrees F for medium.
Step 6: Transfer the roast to a platter or carving board and cover it loosely with aluminum foil. Let the roast rest for 10 to 15 minutes before carving and serving. The easiest way to carve the roast is to cut it into rib sections using a long, slender knife, then slice it into thin slices to serve.
When buying prime ribs, be sure to choose a roast with a thick jacket of fat. The fat melts as the roast cooks, basting and tenderizing the meat.
If you can’t find fresh rosemary, the beef will have plenty of flavor grilled with dried rosemary.