Published March 1, 2013. From Cook's Illustrated.
Swapping in a butterflied leg of lamb for the usual bone-in or boned, rolled, and tied leg options provided us with a number of benefits: thorough seasoning, a great ratio of crust to meat, and faster, more even cooking. By first roasting the lamb in a 250-degree oven, we were able to keep the meat juicy, while a final blast under the broiler was all it took to crisp and brown the exterior. We ditched the usual spice rub (which had a tendency to scorch under the broiler) in favor a slow-cooked spice-infused oil that both seasoned the lamb during cooking and provided the basis for a quick sauce.
We prefer the subtler flavor and larger size of lamb labeled “domestic” or “American” for this recipe. The amount of salt (2 tablespoons) in step 1 is for a 6-pound leg. If using a larger leg (7 to 8 pounds), add an additional teaspoon of salt for every pound.
1. FOR THE LAMB: Place lamb on cutting board with fat cap facing down. Using sharp knife, trim any pockets of fat and connective tissue from underside of lamb. Flip lamb over, trim fat cap so it’s between 1/8 and 1/4 inch thick, and pound roast to even 1-inch thickness. Cut slits, spaced 1/2 inch apart, in fat cap in crosshatch pattern, being careful to cut down to but not into meat. Rub 2 tablespoons salt over entire roast and into slits. Let stand, uncovered, at room temperature for 1 hour.
2. Meanwhile, adjust oven racks 4 to 5 inches from broiler element and to lower-middle position and heat oven to 250 degrees. Stir together oil, shallots, garlic, ginger, rosemary, coriander seeds, bay leaves, lemon zest, and pepper flakes on rimmed baking sheet and bake on lower-middle rack until spices are softened and fragrant and shallots and garlic turn golden, about 1 hour. Remove sheet from oven and discard bay leaves.
3. Thoroughly pat lamb dry with paper towels and transfer, fat side up, to sheet (directly on top of spices). Roast on lower-middle rack until lamb registers 120 degrees, 30 to 40 minutes. Remove sheet from oven and heat broiler. Broil lamb on upper rack until surface is well browned and charred in spots and lamb registers 125 degrees, 3 to 8 minutes for medium-rare.
4. Remove sheet from oven and, using 2 pairs of tongs, transfer lamb to carving board (some spices will cling to bottom of roast); tent loosely with aluminum foil and let rest for 20 minutes.
5. FOR THE SAUCE: Meanwhile, carefully pour pan juices through fine-mesh strainer into medium bowl, pressing on solids to extract as much liquid as possible; discard solids. Stir in mint, parsley, shallot, and lemon juice. Add any accumulated lamb juices to sauce and season with salt and pepper to taste.
6. With long side facing you, slice lamb with grain into 3 equal pieces. Turn each piece and slice across grain into 1/4-inch-thick slices. Serve with sauce. (Briefly warm sauce in microwave if it has cooled and thickened.)
Configured for Easy Carving
First position the meat so that a long side is facing you. Then slice the lamb with the grain into three equal pieces. Turn each piece so that you can now cut across the grain, and cut into 1/4-inch-thick slices.
A Better Way to Spice Up Lamb
Rather than rub spices and aromatics on the lamb’s surface, where they can burn, we bloom them on a baking sheet and then roast the meat on top. The lamb protects the spices and picks up flavor.
1. Bloom spices and aromatics.
2. Place lamb on top to roast.
3. Use flavored oil to make sauce.