Prime rib, also referred to as a standing rib roast, is one of the most prized cuts of beef because of its tender texture and rich flavor. Steven Raichlen and Greg Schneider note in their book, "How to Grill," that prime rib is generously marbled, which lends flavor, but grilling will cook some of it off so you do not end up with a greasy plate of meat. The best way to create a tender and juicy prime rib is to cook it slowly over low heat. Typically served with horseradish or Yorkshire pudding, a grilled prime rib can become a gourmet meal.
Preheat your outdoor grill to medium high. Rinse your prime rib with cool water and pat dry.
Cut each clove of garlic into four slices. Make several small slits in the prime rib using a sharp knife. Insert one piece of garlic into each slit.
Season all sides of the prime rib with salt, pepper, rosemary and garlic powder. Place the prime rib on the grill and cook over medium high heat until seared and golden brown. Flip the prime rib and sear the other side as well.
Reduce the heat to medium and move the prime rib to an upper rack away from direct heat. Close the lid tightly and allow the prime rib to cook for one hour to an hour and 30 minutes, depending on thickness.
Poke an instant read meat thermometer into the fattest part of the prime rib to check for doneness. The thermometer should read 135 degrees F. for a medium prime rib, 145 degrees F. for a medium-well prime rib and 155 degrees F. for a well done prime rib.
Take the prime rib off the grill using a pair of tongs and transfer to a large serving platter. Slice with a sharp knife and serve with horseradish sauce for dipping.