Lightly coat the lamb with the oil. Using the tip of a small, sharp knife make shallow slits all over the surface of the lamb. Remove 4 cloves from the garlic head, peel them, thinly slice them lengthwise, and then push a slice into each slit. Pull off small sprigs from the rosemary bunch and push a sprig into each slits. Allow the roast to stand for 30 to 40 minutes before grilling.
Prepare the grill for direct cooking over medium-high heat (400° to 500°F).
Prepare the grill for cooking over medium-high heat (450°F)..
Sear the lamb over direct medium-high heat, with the lid closed, until nicely browned on all sides, 10 to 15 minutes, turning every few minutes.
Sear the lamb over medium-high heat, with the lid closed, until nicely browned on all sides, 10 to 15 minutes, turning every few minutes.
Meanwhile, scatter the carrot, onion, and the remaining unpeeled garlic cloves and rosemary in a large foil pan and pour in the wine and stock. When the lamb is ready, transfer it to the foil pan.
Prepare the grill for indirect cooking over medium heat (350° to 450°F).
Prepare the grill for cooking over medium heat (400°F).
Place the foil pan on the cooking grates over indirect medium heat and grill, with the lid closed, until an instant-read thermometer inserted into the thickest part of the leg away from bone registers 125°F (or your preferred doneness), about 1 1/2 hours for medium rare, turning once. Remove the lamb from the grill to a cutting board, tent with aluminum foil, and let rest at room temperature, indoors, for about 15 minutes before carving.
Place the foil pan on the cooking grates over medium heat and grill, with the lid closed, until an instant-read thermometer inserted into the thickest part of the leg away from bone registers 125°F (or your preferred doneness), about 1 1/2 hours for medium rare, turning once. Remove the lamb from the grill to a cutting board, tent with aluminum foil, and let rest at room temperature, indoors, for about 15 minutes before carving.
While the lamb rests, make the pan juices. Pour the contents of the drip pan through a fine-mesh sieve held over a medium saucepan. Discard the contents of the sieve. The liquid should be rich, slightly thick, and have a great lamb flavor. Place the pan over indirect heat on the grill to keep warm, skimming off any fat from the surface before serving. If you prefer a more concentrated flavor, place the pan over direct heat on the grill and simmer until reduced as desired, skimming off any fat that rises to the surface.
Carve the lamb and serve with the warm pan juices.
