A traditional roast leg of lamb is a beautiful piece of meat. Served alongside roast veggies, maybe some steamed asparagus, it’s a fine and delightful centerpiece to any holiday feast, especially Easter. But if you want to freshen up your holiday feast while also getting dinner to the table much more quickly, then you should try making this grilled butterflied leg of lamb. It’s a beautiful presentation in its own right and is actually tastier than a traditional leg. Here we’ll give you the thermal lowdown and the temp tips you need to get perfectly rosy lamb to the table in record time.
Why butterfly leg of lamb?
The more time I spend with the grill and the smoker, the more I find that butterflying meats is one of the greatest hacks there is. Butterflied (spatchcocked) chicken is fantastic, and butterflied pork butt will get you better-tasting pulled pork in only 4–5 hours. Well, the same is true for a leg of lamb.
By butterflying a boneless leg of lamb, you decrease the distance from the surface of the lamb to the thermal center, meaning you don’t have to pump heat into it for as long a time to get the thermal center up to temperature. It cooks faster. But there’s more to it than that. By decreasing the thermal distance, we also reduce the thermal gradients in the meat, meaning that we get a more even cooking.
To illustrate this, imagine the amount of heat that has to cross the border of the meat in order to cook it all the way to the center. In a thicker cut, more “bits” of heat will cross that surface in order to heat every bit of meat into the center. But in a thin cut, fewer tiny heat soldiers have to invade the meat to conquer the whole territory. Since there has been less “foot traffic” (thermal traffic) passing through the first few millimeters of meat, those millimeters are less likely to overcook. As long as you don’t force too much heat into the meat too quickly (we’ll talk about that in a minute) it should be nice and uniform.
But wait! There is yet another reason to butterfly your lamb: flavor. The fat-football shape of a leg of lamb provides relatively little surface-to-volume ratio, so there isn’t much seasoning per mouthful of meat. But if you take a lot of the inside and put it on the outside by flaying the thing out flat, you vastly increase the amount of seasoning per mouthful. There are few bites on the finished product that don’t have a piece of grilled, seasoned/salted surface, so it’s far tastier than its nearly spherical cousin.
Temperatures for butterflied leg of lamb
While the USDA encourages us to cook your lamb to 145°F (63°C), I much prefer my lamb cooked to medium-rare, 130–135°F (54–57°C). If you like yours done more (or less), you can certainly do that. No matter your desired doneness, you can get there easily with a two-stage cook.
If you have a large grill, set it up for two-zone cooking with a direct-heat side and an indirect-heat side. We were using a large kamado-style grill, so we made our coal bed for direct cooking, then, when the time came, put in our deflector plates to create an indirect-heat environment.
To cook the lamb, first smear it with the rub described below, then grill it over direct heat until it is nicely browned with bits of char on it. This will give you depth of flavor. Once the outside is nicely browned, move your meat to indirect heat. We used our Smoke X2™ multi-channel thermometer hooked up to our Billows™ BBQ Temperature Control Fan to keep our grill running at 250°F (121°C), a perfect temperature for easing the meat up to its final doneness temp. We set the high-temp alarm on the meat-probe channel to 130°F (54°C) so that it sounded as soon as the leg of lamb headed into medium-rare territory. With such a low cooking temp and such a thin piece of meat, there is very little carryover cooking, so don’t plan on the temp going too much higher than your pull temp. It took a little over an hour to cook through.
Verify the temps in the butterflied leg, of course, with your Thermapen® to make sure it’s done everywhere. Turn and rotate the leg as needed to get it done evenly. Or, don’t and let there be rarer slices for those that like it that way. That’s not a bad move, but you should know where they are, and the Thermapen will help with that.
Seasoning grilled leg of lamb
You can season your lamb with any number of cultural flavor palates, but I like using a wet rub of herbs for it. We used fresh mint, fresh parsley, an onion, some vinegar, some chili, and some black pepper which we made into a paste in the blender. We scored the fat cap on the leg to get good adhesion and penetration and rubbed the paste into all the nooks and crannies. This ended up even better than expected because as the onion in the paste cooked, it sweetened (as onions do) and added another layer of flavor to the roast.
And look, I know mint jelly is generally frowned upon, but some kind of mint sauce is a terrific accompaniment. (Even though we’ve minted the surface already, the fresher, uncooked mint flavor is very welcome) Try putting the leaves from one bunch of mint into a blender with 2 tsp vinegar, 1/2 tsp kosher salt, 2 tsp sugar, and enough water so that the blender can do its thing (1/2-ish cup). Whiz it all together until it is a bright green, thin liquid. Spoon it onto your lamb either on the serving plate or on your own plate and relish the flavor.
I love lamb, and I hope that you’ll give this recipe a shot. Its unique flavor, mingled with the mint and onion and chili, is a real treat that any meat lovers at your table are sure to enjoy. Follow our thermal tips by monitoring critical temps, butterflying, searing, and then finishing it over low heat. You will get just the doneness you want and I think you’ll be glad you tried it.
Oh, and if you want to use this as one piece in an Easter buffet, you could also cook up a double-smoked, glazed ham and some smoked deviled eggs to serve it with. Throw on some pickled asparagus and pickled radishes, some charred grilled carrots and beets, and some fresh homemade bread and you’ve got a buffet that will not soon be forgotten.
Butterflied Leg of Lamb: Seared, Then Slow, For Perfect Doneness
Grilled butterflied leg of lamb, inspired by Dad Cooks Dinner and Saveur,
- 1 boneless leg of lamb, about 5 lb (you can have your butcher butterfly it for you if you like)
- 1 bunch fresh mint
- 1 bunch fresh parsley
- 1 onion, very coarsely chopped
- 2 tsp apple cider vinegar
- 1 tsp ground black pepper
- 1 tsp red pepper flakes or dried red pepper such as Aleppo or gochugaru
- 3 Tbsp olive oil
- Kosher salt
- Preheat your grill and prepare it for two-zone cooking or, as in our case, have a deflector plate of some kind handy to provide indirect heat when the time comes.
- Butterfly the lamb leg by flopping it as wide open as you can and cutting parallel to the cutting board through the thicker muscles, just leaving them attached enough to stay a part of the whole. Again, you can have your butcher do it if you like.
- Prepare the seasoning rub by combining the mint leaves (plucked from the tough stems), parsley, coarsely chopped onion, vinegar, chili, black pepper, and olive oil in a blender and blending until you have a smooth paste. Add more oil if necessary to make a loose, smearable paste.
- Score the fat cap on the lamb if there is one, by cutting a cross-hatch into the fat, trying not to cut the meat underneath it.
- Season the lamb generously with kosher salt, then apply the mint rub and work it into all the creases and nooks.
- Move to the grill and cook the leg of lamb for about five minutes per side, until the exterior is nicely browned and there are some charred bits on it.
- Move the meat to the indirect-heat side of the grill or change your grill setup for indirect heat.
- If there is any herb rub left from before, smear it on now.
- Use the air probe from your Smoke X2 to monitor the heat, and try to maintain a temperature of about 250°F (121°C). If you’re not using a gas-powered grill, Billows will help a lot!
- Insert the meat probe from the Smoke X2 into the lamb and set the high-temp alarm for 130–135°F (54–57°C) for medium-rare lamb.
- Close the lid and cook, about 60–70 minutes, until the alarm sounds. Verify the doneness with your Thermapen and remove the meat from heat to rest.
- Carve and serve to great admiration.
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Karen Duarte says
Very nice recipe- may try in the future. But this year we will place the lamb in a rack and rotisserie it with just garlic and herbs de Provence rub.
Had success with chops doing this so we’ll try it with the leg.
and have your recipe for future use- once my fresh mint is ready!
John deamos says
I have3 a WEBER gas grill. . How long will a 4 lb., butterflied leg of lamb take using this recipe?
Due to the geometry of the ting, it will take about the same time. Plan on about an hour.
Brent Thorley says
Tried this with a deboned leg of lamb and fresh mint from my parents garden. It was outstanding!!!
We did both the mint and parsley rub and the mint sauce. We had to add a little more sugar, 1 tsp, to the mint sauce for our tastes.
I cooked this on a Traeger using Oak. For salt, I’m finding 1 tsp Kosher salt per pound works well. The rubbed lamb was in the refrigerator just before cooking, so the total cook time was extended to almost 2 hours. I targeted 140F. (My parents grew up in Utah around lamb and sheep, and this was about the rarest they can take.) This was a similar cook time to the mini Prime Ribs that I started cooking last year.
This ended up being a truly gourmet meal!
Thank you Martin Earl! I really appreciate your science behind the cook, and for allowing me to produce some outstanding meals at home.
Wonderdul to hear! So glad you liked it.