Make the marinade for the lamb leg - very finely chop the rosemary leaves, mince the garlic and press onto it with the flat side of the knife, zest the lemon. Combine all three with the olive oil, Dijon mustard and salt and pepper. Mix well.

Trim any excess fat from the leg of lamb, leaving a good fat cap on top. Score the fat cap in a diamond pattern until you just reach the meat. Apply the marinade paste all over the lamb, rub it in the scored parts. Place onto a plate, season with salt and pepper and cover*. Marinate refrigerated from 4 hours to overnight.

Bring the leg of lamb to room temperature (about 30-40 minutes on the counter) and preheat a charcoal** grill to 325F. No need to scrape off the marinade paste - it will help form a flavorful crust.

Place the leg of lamb directly onto the grill rack, over indirect heat, fat cap facing up. Turn it over/reposition it every 20 minutes or so to expose all surfaces to the indirect heat and the grill rack. Do so last for the side with the fat. Maintain a constant grill temperature and grill until a meat thermometer inserted in the thickest part registers 135 F for medium-rare. If you'd like a section of the lamb leg to be cooked medium (as seen in the pictures) grill the meatiest side of the leg until the temperature there is 140-145F. *** Allow the lamb to rest onto a board for 10-15 minutes before you carve it. You may loosely tent it with foil to keep it warm.