How to Make It
Set the lamb on a work surface. In a small bowl, combine the piment d’Espelette with the grated garlic, the thyme, 1 1/2 tablespoons of kosher salt and 2 tablespoons of the oil to form a paste; rub the paste all over the lamb. Roll up the lamb and tie with kitchen string at 1-inch intervals; wrap in plastic and refrigerate overnight.
Unwrap the lamb and bring it to room temperature. Preheat the oven to 500°. Place the lamb in a large enameled cast-iron casserole and roast for 20 minutes, until browned on the bottom. Turn the lamb over and roast for another 10 minutes. Add the sherry and 1 cup of water and cover. Reduce the oven temperature to 225° and braise the lamb for 2 hours. Add the onions, cover and cook for 1 hour longer.
Uncover the casserole and cook for about 30 minutes, until the onions have softened and the lamb is fork-tender. Remove the casserole from the oven and stir in the dates. Let stand at room temperature for 20 minutes. Spoon off as much fat as possible from the juices.
In a large skillet, heat the remaining 1/4 cup of oil. Add the halved garlic cloves and cook over high heat, stirring, until they are lightly golden, about 1 minute. Add the kale, season with kosher salt and cook, tossing, until just tender, about 4 minutes.
Remove the strings from the lamb and carve the meat into thick slices. Transfer the kale to shallow bowls and top with the lamb. Spoon the onions, dates and juices all around. Garnish with the almonds and orange zest, sprinkle with sea salt and pepper and serve right away.
Piment d’Espelette is available at specialty food shops, spice shops and piperade.com.