1/2 cup horseradish mustard
2 tablespoons Worcestershire sauce
4 cloves garlic minced
Coarse ground salt and black pepper to taste
Preheat your grill to 225 degrees F. While the grill is warming up, prepare your roast. Trim any excess fat from the top of the roast down to 1/4 inch thick. In a small bowl combine the mustard, Worcestershire sauce and garlic. Slather the entire roast with the mustard mixture and season liberally with the salt and pepper. Place the roast on the grill and close the lid. Smoke until the internal temperature of the roast reaches 120 degrees F for Rare or 130 degrees F for Medium. For a rare, bone-in roast, plan on 35 minutes per pound of prime rib. Remove the roast to a cutting board, cover the roast with foil, and allow to rest for 20 minutes. While the roast is resting, increase the temperature of your grill to 400 degrees F. Once the grill is up to temperature, return the roast to the grill and sear until you reach your desired internal temperature. Pull the roast off at 130 for rare, 135 for medium rare, 140 for medium. This process should go quickly, so keep an eye on your temperature. Remove your roast to the cutting board and let the meat rest for at least 15 minutes before slicing and serving.