1 boneless leg of lamb, 5 to 6 pounds, butterflied
Methods/steps
Place onion, garlic, rosemary, lemon zest, apple cider vinegar, and olive oil into a food processor and pulse to combine.
Sprinkle a generous amount of salt and pepper over the lamb. Place the onion marinade and lamb into a 1-gallon freezer bag. Spreading the marinade over all sides of the meat. Seal the bag and refrigerate for 1 to 2 hours
After the 1-2 hours, remove lamb from the refrigerator and allow it to come to room temperature, around 20 minutes. When ready to grill, remove the lamb from marinade bag.
Fat side down, place the lamb on the grill on the hot side of the grill
Sear one side for 4 minutes, flip, sear the other side for an additional 4 minutes.
( if you are using a charcoal grill, move the lamb to the less hot side of the grill. Using a gas grill, lower your heat to low. Try to maintain a temperature of 300-350F.)
Cover grill and let cook for 35-45 minutes ,depending on thickness, meat thermometer inserted into the thickest part of the roast registers 130F,for medium rare
Place lamb on a cutting board with a well to catch the juices. Cover with foil and allow to rest for 5-10 minutes. Cut across the grain, 1/4 to ½ -inch thick slices.
Serve slices on a warm platter; pouring the meat juices over the slices.
Additional Tips
To prepare grill. If you are using a charcoal grill, prepare the coals so that they are double layered on only one side of grill, and only sparsely single layered on the other side, called "banked" grilling. Using a gas grill, heat the grill on high with all burners to start. After the initial browning you will reduce heat