The Food Lab: Sous Vide Leg of Lamb With Mint, Cumin, and Mustard

The Food Lab

Unraveling the mysteries of home cooking through science.

20161007-mint-cumin-mustard-sous-vide-lamb-leg-32.jpg

[Photographs: J. Kenji López-Alt]

I tend to prefer bone-in cuts of meat when the bone is easy to work around, as with a prime rib or a juicy roast pork loin. The tastiest bits of meat (read: the fattiest) are typically stuck around the bones.

But leg of lamb is an exception. Not only does the large, irregularly shaped bone make carving neat, against-the-grain slices difficult, it's also a bit too unwieldy to pick up and gnaw on, no matter how uncouth your table manners. Besides, leg of lamb has enough fatty bits that you don't need the ones connected to the bone.

Cooking with a deboned leg of lamb offers another advantage: It's ideal for stuffing and rolling with other ingredients, and, because lamb is so robustly flavored on its own, you don't have to be shy or subtle about it. Slow-roasting it using the reverse-sear method is a fantastic way to get perfectly evenly cooked results after stuffing, but today we're cooking sous vide, which is even more foolproof.

20161007-mint-cumin-mustard-sous-vide-lamb-leg-01.jpg

The idea of pairing lamb with crunchy fried spices is one I saw in action when a friend of mine served me a leg of lamb cooked using this great recipe from ChefSteps. It uses a bone-in leg of lamb covered with a heavy dusting of mustard powder, cooked for 24 hours, then served with a coating of fried mustard seed, caraway seed, and herbs. I loved the way the seeds popped against the tender lamb, but I found that after 24 hours of cooking, the lamb was a little too mushy for my taste. (We first theorized that it might have been because he was using a frozen leg of lamb, but I repeated the recipe with a fresh one and ended up with similar results. I don't recommend cooking leg of lamb sous vide for any longer than six hours.)

I start my recipe by heating some oil up in a skillet, then adding a tablespoon of black mustard seeds and a couple of teaspoons of whole cumin seeds. They should immediately crackle and spit (and your kitchen should smell amazing) as they toast. Stirring them continuously will prevent them from burning in spots. Once their aroma has developed, which takes only a few seconds, I transfer the whole mixture to a bowl, season with salt and pepper, and let it cool until it's just cool enough to handle.

20161007-mint-cumin-mustard-sous-vide-lamb-leg-05-composite.jpg

A full boneless leg of lamb is large, weighing around 10 to 12 pounds. It's too large to fit comfortably in a sous vide bag, so for this, I recommend using half of a deboned lamb leg, which should be in the four- to five-pound range. Start with a butterflied leg of lamb (it's easiest to just ask your butcher to butterfly it for you—deboning a leg of lamb is not a simple task unless you have a very sharp boning knife and plenty of experience), and spread half of the fried spice mixture all over the interior surface before rolling it back up tightly. When seasoning that spice blend with salt, it's important to remember to add enough salt to season the lamb, not just the spices themselves. It should taste quite salty.

20161007-mint-cumin-mustard-sous-vide-lamb-leg-13-composite.jpg

Next, I secure the lamb leg with a few pieces of twine. There's a trick to neatly tying together a rolled roast like this. Tying from one end to the other can push the meat out of shape as it gets squeezed unevenly. Instead, tie it from the outside toward the center, starting with two pieces of twine tied at either end, then working your way inward, alternating sides with each piece of twine to create a nice, evenly cylindrical shape. This helps the whole thing cook and slice more easily as well.

Once it's tied, I season it with salt and pepper and place it inside a zipper-lock bag to cook.

20161007-mint-cumin-mustard-sous-vide-lamb-leg-15.jpg

For my recipe, I use the same temperature chart I used for my sous vide rack of lamb, though, because of its larger size, a leg of lamb requires at least two hours to cook through to the center. But, as I mentioned before, any longer than six hours or so will get you into mushy territory, so I recommend capping the cooking time there.

Sous Vide Boneless Leg of Lamb Temperatures and Timing

Doneness Temperature Range Timing Range
Very rare to rare 115°F (46°C) to 124°F (51°C) 2 to 3 hours
Medium-rare 125°F (52°C) to 134°F (57°C) 2 to 6 hours (3 hours max if under 130°F/54°C)
Medium 135°F (57°C) to 144°F (62°C) 2 to 6 hours
Medium-well 145°F (63°C) to 154°F (67°C) 2 to 6 hours
Well-done 155°F (68°C) and up 2 to 6 hours

Meanwhile, it's time to focus on the sauce. Remember the half of the mustard and cumin seeds we set aside? Those are going to become the base for an herb-packed chimichurri-style sauce. In restaurants, where there's a steady supply of stock on hand at all times, making a classic stock-based sauce for meats is easy. At home, not so much. That's why herb sauces, like chimichurri and Spanish-style salsa verde, are my go-tos. They're fresh and fast, and they offer complexity and depth of flavor without relying on slow-simmered stocks or reductions.

20161007-mint-cumin-mustard-sous-vide-lamb-leg-16.jpg

For this one, I combine my fried seed mixture with a handful of chopped fresh mint and cilantro, some minced shallots and garlic, and a minced red jalapeño chili, whisking it all together with a small splash of red wine vinegar and plenty of olive oil.

Once the lamb has finished with its sous vide bath, it still needs a sear to develop color and flavor on the exterior. A deboned leg of lamb is small enough that you can easily do this in a skillet.

20161007-mint-cumin-mustard-sous-vide-lamb-leg-21-composite.jpg

I remove the lamb from its bag, pat it dry very carefully on all surfaces with paper towels (moisture is the biggest enemy of good browning!), then sear it in a ripping-hot skillet, turning it occasionally to ensure that all sides brown evenly.

One of the benefits of sous vide cooking is that it gives you great flexibility when it comes to serving time. Once your lamb is in the water bath, you can serve it anywhere between two and six hours later, with no real loss in quality. As soon as you're ready, it takes about 15 minutes to dry and sear the lamb, and dinner is served.

20161007-mint-cumin-mustard-sous-vide-lamb-leg-26.jpg

All that's left is trimming off the twine, then slicing it for serving.

20161007-mint-cumin-mustard-sous-vide-lamb-leg-33.jpg

I love the way the mustard and cumin seeds inside the lamb and in the sauce crunch and pop between your teeth, giving you little bursts of flavor as you chew. Meanwhile, the freshness of the herbs offers a nice counterpoint to the intense lamb and earthy spices.

20161007-mint-cumin-mustard-sous-vide-lamb-leg-37.jpg

Of course, you're not obligated to cook this sous vide. Once you've stuffed and rolled the lamb, it'll work wonderfully when cooked using our more traditional roast lamb method, but that sous vide machine just makes it so darn foolproof.