Grilled Butterflied Leg of Lamb

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Where to start? Somehow I suspect that the following method – fat is good, flame is good – is going to get me in trouble with some of you. But since this was the best lamb roast I’ve ever eaten in my life, I will forge ahead and tell you how we did it.

The lamb roast was succulent – crusty, flavorful char on the outside, pink and tender on the inside. Many recipes call for trimming off the excess fat from the lamb roast. I did that once to a prime rib roast and have never forgiven myself. Later I learned from my dear mother that “excess fat” was anything more than an inch thick in her book. The fat is needed to make the lamb tender and tasty. Trim it if you must, but leave some on.

Note that the more fat on the lamb roast, the more likely you’ll have flare-ups when you grill. Flare-ups are okay as long as they are controlled and don’t get out of hand. The charring of the outside of the lamb, especially the fatty side, produces amazing flavor. By the way, it used to be that people were worried about char grilling being carcinogenic. Turns out if you marinate the meat in an acid-based marinade first, you negate the cancer-causing elements. (Grillers everywhere rejoice.)

Some people take offense at the very idea of using mint jelly with lamb. I wouldn’t have lamb without it. Homemade mint jelly is fantastic with lamb. And if we’re out, I’ve been known to chop up some fresh mint leaves just to go with the lamb. So, to each her own when it comes to the jelly. What is your favorite way to prepare leg of lamb?

Grilled Butterflied Leg of Lamb Recipe

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  • Prep time: 1 hour, 10 minutes
  • Cook time: 1 hour

In this recipe we sear the lamb first, on both sides, grilling on high heat for a short amount of time. Then we cook the lamb on lower heat until it is cooked through. In our opinion, the only way to eat lamb is medium rare or rare. There is nothing more depressing than dried-out, over-cooked lamb. For this reason it is essential that you use a meat thermometer to test the internal temperature of the roast.

Ingredients

  • 1/2 onion
  • 4 cloves garlic, peeled
  • 2 Tbsp fresh rosemary leaves, or 1 Tbsp dried
  • Zest of 1 lemon
  • 1 Tbsp apple cider vinegar
  • 2 Tbsp olive oil
  • Kosher salt and freshly ground black pepper
  • 1 boneless leg of lamb, 5 to 6 pounds, butterflied

Method

1 Put onion, garlic, rosemary, lemon zest, apple cider vinegar, and olive oil into a food processor and pulse to combine. (If you don't have a food processor, just chop the onions, garlic, and rosemary very well and combine with the rest.)

2 Sprinkle a generous amount of salt and pepper over the lamb. Place marinade and lamb into a 1-gallon freezer bag. Spread marinade over all sides of the meat. Seal the bag and refrigerate for 1 to 2 hours.

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3 Remove lamb from refrigerator and let come to room temperature (about 20 minutes). When ready to put on grill, remove from marinade bag. To help make the lamb easier to turn on the grill you can insert a couple of skewers through the lamb, crosswise. (A tip learned from Rick Rodgers in Kingsford Complete Grilling Cookbook.)

4 Prepare grill. If you are using a charcoal grill, prepare the coals so that they are double layered on one side of the grill, and sparsely single layered on the other side of the grill (this is called "banked" grilling). If you are using a gas grill, heat the grill on high on all burners to start. After the initial browning you will reduce the heat.

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5 Place the lamb, fat side down, on the grill on the hot side (double layer charcoals). You will get likely get flareups, so be prepared with a squirt bottle of water or a couple of cups of water (if using a charcoal grill) to control the flames if needed. (My brother Matt swears by shaking the bottle of beer he is drinking to squirt some beer on the coals when needed for flareups.) Sear one side for 4 minutes, then flip the lamb over to sear the other side for another 4 minutes. Then, if you are using a charcoal grill, move the roast to the less hot side of the grill. If you are using a gas grill, lower the heat to low. You will want to maintain a temperature of 300-350°F. Cover the grill and let cook for an additional 35-45 minutes (depending on how thick, and how many pounds the roast is), until a meat thermometer inserted into the thickest part of the roast registers 130°F (for medium rare).

6 Transfer to a cutting board with a well to catch the juices. Cover with aluminum foil and let rest for 5-10 minutes. Remove the skewers if you are using any. Cut across the grain, 1/4 to 1/2-inch thick slices. Serve slices on a warm platter; pour meat juices over the slices. Serve with mint jelly or horseradish. Serves 8-10.

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Lamb roast for this recipe generously provided by the American Lamb Board

Links:
Lamb. The better red meat. - Thoughtful essay from Jo of Amuse Bouche, also a recipe for Lamb Korma with almonds, pecans and sour cream.
The Niman Ranch Cookbook: From Farm to Table With America's Finest Meat
Kingsford Complete Grilling Cookbook
Wikipedia on Grilling

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Showing 4 of 30 Comments

  • Michelle Dold

    THANK YOU SO MUCH FOR THIS RECIPE GUIDE!! I followed this exactly and my first leg of lamb for this thanksgiving turned out AMAZING!!!

  • Madeline Scrogin

    I note this recipe was posted by Elise in 2007. I wonder if she still grills her buttered leg of lamb without trimming the fat. I think I have too many years experience both cooking lamb roasts and eating roast lamb all across France (nothing to compare with the salt marsh raised lamb from the western coast of France, especially near St. Michel). I guess this might be the only advantage of ahem, aging! But I would never cook a roast or grilled leg of lamb without trimming the fat and most of the fell away.

    Also it should be noted that marinades might add flavor but they do not “tenderize” lamb. Good pink lamb comes already as tender as it’s ever going to be (go to a quality butcher or market). And only the cook can take that away, ending up with over-cooked dry and chewy lamb.

    My last comment is regarding Elise’s comparison of a prime rib and a lamb roast as a learning experience. I’m afraid this is apples and oranges talk. Of course one never trims a prime rib roast; a good prime rib roast should come already trimmed to perfection by an excellent butcher. (I believe Elise’s mother was referring only to beef steaks, etc. with her comment about 1″ of fat. Lamb fat does not have a good and so it won’t add a good flavor. The opposite might be more true.) The flavor of the lamb roast should come from the lovely pink tender flavor of the meat itself and so even flare-ups are better saved for beef. Flare-ups and even a small fire can really enhance a nice big prime rib. This I know from many years of grilling a 10-12 lb. prime rib, a beautiful specimen, every year for our holiday Christmas party.

  • sue ross

    My boneless leg of lamb is very thick on one side and thin on the other. Should I cook for short side med rare and cut that part off, grilling the thicker side more? I could also flatten the thicker side before cooking.

  • genghisbahng

    Hi — this looks amazing and I’m planning on making this tonight. Other recipes I’ve seen have called for making small cuts in the lamb with a paring knife before marinating. Sounds good, but also like it might allow the meat to dry out? Any thoughts on that? It goes without saying, love the site, have eaten my way through half of it already, and am looking forward to the rest. :)

    I haven’t tried this with lamb, but with pork or beef roasts we make small cuts and insert garlic cloves into the cuts. Turns out beautifully. ~Elise

  • Goldiegal

    As an English woman, I was raised on the most wonderful lamb; roasted lamb, stewed lamb, braised lamb … you name it! I do take issue over your statement that lamb shoud not be cooked more than medium rare, though. If cooked gently it can be well done without being dry and/or tough. I prefer my meat well done and would certainly not put up with dry, unappetizing meat. “Well done” when “done well” means using patience.

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