For this recipe we use what we call a double-bank method, which is perfect for large roasts because it allows you to caramelize the meat on all sides even though you are roasting it over indirect heat. We recommend using two remote thermometers, setting one probe near the meat and one in it. This allows you to monitor the temperatures of the cooking surface and the food. We also love to add hardwood chunks during the cooking process. With the long cooking time, you’ll get wonderful smoke flavor.
This recipe is from the Grill to Perfection cookbook. Click here for a list of places you can buy a copy.
In the bowl of a food processor fitted with a steel blade, combine the rosemary, sage, parsley, garlic, lemon zest, mustard, fennel, and vegetable oil, and pulse to create a paste. Add a bit more oil if the mixture clumps up or is too thick.
Place the lamb on a baking sheet and trim any large pieces of gristle or sinew, leaving most of the fat in place. Smear both sides with the herb mixture. Cover and refrigerate overnight.
Remove the lamb from the refrigerator and prepare the grill for double-bank two-zone grilling. Fill a charcoal chimney with lump charcoal but do not light. Pile half the unlit charcoal to the right and the other half to the left. Set an aluminum drip pan between the charcoal piles and fill halfway with water. Refill the charcoal chimney, stuff newspaper in the bottom of the chimney and light it. When the coals are fully engaged — you should see flames peeking over the top — pour them over the unlit charcoal. Cover the grill and open the vents all the way. If using a gas grill, light the gas and turn on the front and rear, or outside burners, to high.
While the grill is heating, re-truss the lamb. Sprinkle both sides with salt and pepper. Roll the lamb back into a roast-like shape, fat side out, and truss with butcher’s twine.
When the temperature reaches 350 to 400 degrees F, clean the grill grate. Place the lamb on the grill directly above the drip pan and cover the grill. For gas grills, place the lamb over the unlit burner. Grill-roast for 45 minutes, or until the internal temperature registers 120 degrees F for rare (our preference) or 130 degrees F for medium. If necessary, add a couple of small pieces of charcoal to each pile while the lamb is roasting to keep a consistent temperature.
Remove the lamb from the grill and place on a cutting board to rest for 20 minutes. Using kitchen shears, snip away the butcher’s twine. With a carving knife, thinly slice the lamb. Sprinkle with the mint, squeeze on the lemon juice and drizzle with a thin line of olive oil.