We always know when
In a medium mixing bowl, combine the rosemary, garlic, olive oil, Dijon mustard, ground mustard, salt, and pepper and whisk to combine. Place the lamb in a shallow baking dish and, using your hands, rub it all over with the marinade. Cover the dish with plastic wrap and refrigerate for least 2 hours, and ideally overnight.
Heat a gas grill to medium. Make a flat pouch out of a double thickness of foil that will fit nicely to one side of your grill. Place the soaked chips in the pouch, poke a couple of holes in the top of the pouch, and place the pouch on the grill. Once the wood chips start smoking, turn the grill to low and lay the leg of lamb on the grates. Grill the lamb for 2½ hours, turning every 30 minutes to cook evenly, until the internal temperature reaches 145°F. Add more soaked wood chips as needed.
Transfer the lamb to a cutting board to rest for 20 minutes before slicing ⅛ inch thick.
© 2010 All rights reserved. Published by Rodale Books.