Makes 6 to 8 servings
3 to 4 pounds boneless lamb shoulder, preferably with a thick fat cap
2 tablespoons kosher salt, plus more
3 tablespoons whole black peppercorns, toasted and lightly crushed
Olive oil, as needed
3 medium red onions, sliced very thin
10 garlic cloves, smashed or finely grated to paste
2 tablespoons each: tomato paste, Dijon mustard
1/4 cup anchovy paste
2 tablespoons rosemary leaves, finely chopped
1 tablespoon smoked paprika (pimentón)
1/2 cup red wine vinegar
1 cup fruity red wine
1 tablespoon agave or honey
1 quart lamb or chicken broth
1. Score, tie, and dry-brine the lamb: If your lamb shoulder does not come with a thick fat cap, skip this step. Place lamb on clean work surface so its fat side faces up. Hold a very sharp knife at a 45-degree angle over one of the fat cap's corners. Score the fat on a diagonal, running the blade from the top corner down and across. When scoring, make sure not to cut through into the meat; each incision should just barely cut into the fat, about 1/8-inch deep. Continue scoring the fat, spacing incisions 1/4-inch apart. Stop scoring where the fat begins to taper off. Working in the opposite direction, repeat the scoring so a tight diamond pattern forms across the fat cap.
Season the lamb on all sides with 2 tablespoons of salt and the pepper. Tie the lamb up with butcher's twine, using a standard butcher's loop at 1-inch intervals. The tied shoulder should form a uniform cylinder. Place the shoulder on a cooling rack set over a rimmed baking sheet. Dry-brine the shoulder, uncovered, in the refrigerator for 12 to 24 hours.
2. Build the braise: Remove the lamb from the refrigerator. Set a large Dutch oven over medium-high heat and swirl 2 tablespoons of olive oil (1/4 cup if shoulder does not have a fat cap). When the oil is hot, lay in the lamb, fat side down. Sear the fat cap, lowering the heat to prevent scorching, for about 10 minutes, or until it crisps and browns deeply. Rotate, lightly searing all sides of the shoulder until they easily release from the pot and are a light golden brown. Transfer lamb to a rack and set aside. Pour off all but 2 tablespoons of fat from the pot, be sure to keep the "fond" in place. Set pot back over medium-low heat and stir in the onions, scraping up all the fond on the bottom. Gently stew the onions for 45 minutes, or until they collapse and caramelize richly. Stir frequently so they color evenly.
3. While onions cook, make the anchovy paste: remove fillets from jar and smash to a paste with a mortar and pestle, or hand-chop finely, adding oil back in as needed to form a smooth paste.
Preheat oven to 325 degrees F. Stir the garlic into the onions and cook for about 10 minutes. Stir in the tomato paste and mustard and sauté for 2 minutes, until paste cooks into the onions. Add the anchovy paste, rosemary, and pimentón. Raise the heat to medium-high. Pour in the vinegar, wine, and agave. Simmer for 15 minutes, or until the liquid turns syrupy and the onions are spreadably soft. Season with salt to taste. Return lamb shoulder to the pot with its fat cap facing up. Spoon and smear the jam all over the lamb and pour in enough broth to cover two-thirds of the shoulder. Bring the broth to a simmer, then reduce to a lazy bubble. Cover the pot and transfer to center rack of the oven. Braise the lamb for 11/2 hours, or until the center is easily pierced with a knife but the meat is still bouncy when prodded. Every 30 minutes, baste the lamb, re-cover, and rotate the pot 90 degrees.
Finish and serve: Remove the pot from the oven and thoroughly baste the lamb shoulder with the juices and caramelized onions. Season with salt to taste. Re-cover and let the lamb rest for 30 minutes. (At this stage, you can cool it and keep it overnight; rewarm it gently in its own juices.) To serve, transfer lamb to a cutting board and remove the twine. Cut the meat into thick slices and arrange them on a warm platter. Spoon juices over top and serve. Excellent with a salad of butterleaf lettuce tossed with warm black-eyed peas (or beans) glazed in warm, lemony butter.