Rub the meat generously with the Spice Rub, coating all surfaces. Refrigerate the Prime Rib overnight before grilling.
Remove the meat from the fridge and allow the roast to stand at room temperature 45 minutes before grilling.
Preheat the grill to high, then turn down the barbecue to low heat. Place a disposable metal pan underneath the roast, beneath the grates, to catch the drippings while cooking. Place the Prime Rib on the grill and cook over indirect medium heat for about 2 hours. The internal temperature for a medium-rare roast is 120°F while still cooking. Remove the roast from the grill, along with the pan of drippings, and place the roast in the pan to rest. Let the Prime Rib stand for 20 minutes before carving. While the roast is resting, make the sauce.
Heat the olive oil in a saucepan and sauté the shallot until translucent. Add the beef broth and coffee and bring to a simmer. Cook until reduced by one-third. When the roast is rested and all the juices have accumulated in the pan, skim the fat off the top and strain the juices through a fine mesh strainer. (You should have about 1/4 cup). Add the arrowroot to the strained drippings and blend thoroughly to make a "slurry”. Add the slurry to the sauce, stirring constantly until the sauce returns to a simmer and begins to thicken. Add the cream and Bourbon and season with salt and pepper to taste. Serve the Sauce with the Prime Rib.
Serves 6 to 8