I wound up not finding the black mustard seeds in time and used just cumin. I heated 1.5 tablespoons (I think) of cumin in a good bit of vegetable oil. I did not do a good job tying the leg of lamb up. The vacuum bags I had were too small for the roast but it worked out. I would do a longer sear on the fat the next time. I don’t think the fat was properly melted. The flavor was very good. Lots of cumin and good saltiness. It pervaded the meat. It was quite chewy and it didn’t help we didn’t have even plastic knives. But it was medium rare through and through and the flavor was very nice.

I want to try this again when I have a chance. I would also pick a smaller roast unless I find larger bags.

http://www.seriouseats.com/2016/10/the-food-lab-sous-vide-leg-of-lamb-mint-cumin-black-mustard.html

3 hours @ 132°F

• 3 tablespoons (45ml) vegetable or canola oil, divided
• 1 tablespoon (12g) whole black mustard seeds
• 2 teaspoons (8g) whole cumin seeds
• Kosher salt and freshly ground black pepper
• 1/2 butterflied boneless leg of lamb (4 to 5 pounds; 1.8 to 2.2kg) (see note above)
• 1 ounce (30g) picked fresh mint leaves (about 1 cup), finely chopped
• 1 ounce (30g) picked fresh cilantro leaves and tender stems (about 1 cup), finely chopped
• 1 small shallot, finely minced
• 1 medium clove garlic, finely minced
• 1 red jalapeño or Fresno chili, finely minced
• 1 tablespoon (15ml) red wine vinegar
• 3 tablespoons (45ml) extra-virgin olive oil

1. Heat 2 tablespoons (30ml) vegetable oil in a small skillet over medium-high heat until shimmering. Add mustard and cumin and cook, stirring constantly, until fragrant, about 30 seconds. Immediately transfer to an empty skillet or heatproof bowl and let rest until cool enough to handle. Season mixture generously with salt and pepper.

2. Spread half of spice mixture evenly over inside of lamb leg, then carefully roll it back up.

3. Secure lamb leg with butcher’s twine at 1- to 1 1/2–inch intervals, starting from both ends and working toward the center. Season exterior generously with salt and pepper.

4. Preheat a sous vide water bath to desired temperature according to chart above. Seal lamb inside a vacuum bag, or a zipper-lock bag using the water displacement method, then submerge and cook for desired time according to chart above.

5. Meanwhile, make the chimichurri by combining remaining cumin and mustard mixture with mint, cilantro, shallot, garlic, chili, red wine vinegar, and olive oil in a medium bowl. Stir vigorously with a fork and season to taste with salt and pepper. Set aside.

6. When ready to serve, remove lamb from bag and carefully pat dry with paper towels. In a cast iron, carbon steel, or nonstick skillet, heat remaining 1 tablespoon (15ml) vegetable or canola oil over high heat until lightly smoking, then add lamb and cook, turning occasionally, until well browned on all sides, about 4 minutes total.

7. Remove twine, slice lamb, and serve immediately with chimichurri.