Prep time: 15 minutes
Cook time: 1 hour and 15 minutes
Prepare the lamb at least 12 hours ahead and up to 2 days in advance. Trim excess fat and remove silver skin using a sharp knife. Score the top layer of fat in a 1/2″ crosshatch pattern, being careful not to slice into the flesh. Using a meat pounder, or the back of a heavy skillet, pound the butterflied lamb leg so it is relatively even. Season all sides very liberally with Kosher salt.
Make the marinade paste by blending all marinade ingredients together with an immersion blender or food processor or use a mortar and pestle. Spread the paste all over the lamb leg on a sheet pan. Cover tightly with plastic wrap and refrigerate for 12 hours or preferably 24 hours.
Remove the lamb from the refrigerator to temper for about 30 minutes while you set up the grill. Insert a remote thermometer probe through the side of the thickest part of the meat.
Prepare the grill with a two-zone setup and bring the temperature up to 400° F. Preheat and add wood chips for extra smoke if desired. Clean and oil the grill grates using a canola oil-soaked paper towel and tongs. Sear the leg (fat side down first) on the hot side of the grill for about 4 minutes per side to get a flavorful golden crust, then transfer to the cooler side of the grill and close the lid.
Continue to cook to an internal pull temperature of 125 to 130°F for medium-rare** (will finish at 130-140° F) or 130 to 135° F for medium (will finish at 135-145° F). This will be approximately 12 minutes per pound. Use an instant-read thermometer to verify doneness. The temperature will continue to rise 5 to 10 degrees after it is off the grill, so pull from the grill before it reaches the desired finished temperature.
Transfer to a cutting board and rest for 15 to 20 minutes.
Carve the lamb leg by slicing against the grain.
**The USDA recommends a minimum internal temperature of 145 degrees F (62.8 degrees C) with a 3-minute rest.
Carryover cooking: The lamb leg will continue to rise in temperature 5 to 10 degrees after it is off the grill, so remove it from the heat prior to the desired finished temperature. If you are experiencing flare-ups while searing, move the lamb to the cooler side of the grill and close the lid.
Want it extra smoky? Add some apple or cherry wood chips to the fire.
Figure 6 to 8 ounces of cooked lamb per person.