Generous 1/4 cup Kosher salt
2 tablespoons sugar
1 teaspoon fennel seeds
1 teaspoon black peppercorns
1 teaspoon allspice berries
1 head garlic, halved crosswise
1 cup dried chickpeas
1 teaspoon baking soda
1 bone-in square-cut lamb shoulder (about 5 pounds)
1/2 cup pomegranate molasses
Persian Rice, optional
Pomegranate Molasses
Combine the salt with the sugar, fennel seeds, peppercorns, allspice, garlic and about 2 quarts water in a large pot. Bring to a rapid boil, stirring to dissolve the salt. Remove from the heat and allow the brine to cool completely.
Combine the chickpeas with the baking soda in a large bowl and cover with water by several inches. Let soak overnight.
Put the lamb shoulder in a large (6- to 8-quart) container and pour the brine over the lamb. (Ideally, the lamb shoulder should be submerged, so weight it with two plates. But if that's impractical, cover the lamb with a clean cloth that's saturated in the brine.) Refrigerate the lamb shoulder in the brine overnight or up to 48 hours.
Preheat the oven to 475°F. Place a rack on a baking sheet. Drain the lamb and pat dry. Put the lamb on the rack and roast until well browned on the exterior, about 30 minutes. (Or sear the lamb over a medium-hot grill for 15 minutes until well browned on all sides and nicely charred in places.) Lower the oven to 300°F.
Transfer the lamb shoulder to a large roasting pan. Mix the pomegranate molasses with 8 cups water in a bowl and add to the pan. (The liquid should come about halfway up the shoulder; add water if needed.) Drain the chickpeas and add them to the liquid. Place a sheet of parchment paper over the lamb and cover the pan tightly with foil.
Braise in the oven until the lamb shreds easily with a fork and the chickpeas are tender, about 5 hours. Let the lamb cool in its braising liquid in the refrigerator overnight.
The next day, preheat the oven to 475 °F. Roast the lamb, uncovered, spooning the braising liquid over the lamb every 5 minutes, until the lamb is hot through and glazed with the liquid, about 30 minutes. Serve with crispy Persian rice if you like.