Serves: 10 to 12 // Prep time: 15 minutes | Standing time: 1 hour | Grilling time: about 2 hours | Special equipment: 2 large disposable foil pans, instant-read thermometer
1 boneless rib roast, about 5½ pounds, trimmed of excess fat
Freshly ground black pepper
½ cup Dijon mustard
½ cup finely chopped shallots
6 garlic cloves, minced or pushed through a press
2 teaspoons finely chopped fresh thyme leaves
2 pounds meaty beef bones
1½ cups low-sodium beef broth
Season the roast evenly with 2 teaspoons salt and 1 teaspoon pepper. Combine the mustard, shallots, garlic, and thyme. Set aside ¼ cup of the mustard mixture for the au jus. Spread the remaining mustard mixture all over the top and sides of the roast. Allow the roast to stand at room temperature for 1 hour before grilling
Prepare the grill for direct and indirect cooking over medium heat (350° to 375°F).
Place one large disposable foil pan inside of the other to create a single pan of double thickness. Put the bones in the pan and set the roast on top of the bones, fat side facing up. Position the pan on the cooking grate with the thicker end of the roast facing the hottest area of the grill. Grill over indirect medium heat, with the lid closed, until an instant-read thermometer inserted into the thickest part of the roast registers 120°F for medium rare, about 2 hours, rotating the roast once after 1 hour. Start checking the temperature of the roast after 1¼ hours. Keep the grill’s temperature between 350° and 375°F.
Remove the pan and the roast from the grill, loosely cover the roast with aluminum foil, and let rest for 20 to 30 minutes (the internal temperature will rise 5 to 10 degrees during this time).
Transfer the roast to a cutting board. Remove the bones from the pan and discard. Pour off and discard the clear fat, leaving the browned bits in the pan. Return the pan to the grill over direct medium heat. Cook until the contents sizzle. Add the broth and the reserved mustard mixture. Holding the pan with an insulated barbecue mitt and using a wooden spoon, scrape up any browned bits from the bottom of the pan. Continue cooking until the mixture is hot. Remove from the grill and season with salt and pepper.
Cut the roast into ½-inch slices. Serve warm with the sauce.