This hearty dish features Middle Eastern flavors, including sumac, which has a tangy taste.
Heat oven to 250 degrees. In 7-quart flameproof casserole or Dutch oven over medium heat, heat vegetable oil until hot but not smoking. Sprinkle salt and pepper generously over lamb shanks. Working in batches if necessary to keep them from touching during the initial searing, add shanks to pan (they should sizzle the moment they hit the pan). Cook lamb shanks until well browned on all sides, 10 to 15 minutes each side. Set browned lamb aside in a large bowl.
Meanwhile, in a small saucepan over medium-high heat, bring the chicken stock to a boil. Add the sumac, and stir to combine; set the mixture aside.
Add onion to the casserole, and cook over medium heat until softened and golden, 5 to 10 minutes. Add reserved stock mixture, apricot nectar, cinnamon stick, cloves, allspice, parsley, cilantro, tarragon, mint, and paprika; stir to combine.
Return the reserved browned lamb shanks to the casserole. Place over medium-high heat, and bring the liquid in the casserole to a boil. Cover the pan, and transfer the casserole to the oven. Cook the mixture until the meat is tender, about 2 hours. Check the casserole in the oven occasionally to ensure a gentle simmer of the sauce, adjusting the heat of the oven or the height of the oven rack as necessary. The actual cooking time will vary depending on the size of the lamb shanks you started with. The meat should be very tender but should not fall off the bone, yet. Add the dried apricots, prunes, and chopped red bell pepper to the casserole, and continue to cook in the oven until the fruit has softened, about 1/2 hour more.
Remove the cooked lamb shanks, apricots, prunes, and bell pepper from the casserole, and place them in the bowl with the lamb. Cover them with aluminum foil to keep warm, and set aside.
Place the casserole over medium heat, and simmer until the liquid is thickened and reduced, about 15 minutes. Return the reserved lamb shanks, apricots, prunes, and bell pepper to the casserole just long enough to heat them through again, and stir them lightly to coat them with the sauce. Season with salt and pepper. Serve lamb shanks and sauce with couscous with mint and lemon.