How to Make It
In a nonreactive medium saucepan, boil the pomegranate juice over high heat until reduced by half, about 15 minutes. Let cool to room temperature.
In a blender or food processor, puree the pomegranate juice with the mint, peeled garlic cloves and grenadine. Put the lamb shanks in a large glass or ceramic dish and pour the marinade on top. Cover and refrigerate for at least 12 and up to 24 hours, turning the shanks occasionally.
Preheat the oven to 375°. Heat the oil in a large, heavy, nonreactive skillet. Drain the lamb shanks and pat dry. Season them liberally with salt and pepper. Add 2 or 3 shanks at a time to the skillet and cook over moderately high heat, turning, until well-browned all over. Transfer the shanks to a roasting pan just large enough to hold them all.
Reduce the heat under the skillet to moderate and stir in the carrots, onions and halved garlic heads. Cook until the onions just soften, about 3 minutes. Add the wine, increase the heat to moderately high and scrape up any browned bits that are stuck to the pan. Boil until the wine is reduced to 1 cup, about 7 minutes. Stir in the tomatoes and pour the mixture over the lamb shanks. Add the chicken stock and enough water to submerge the shanks by two-thirds. Season with salt and pepper. Cover the roasting pan with foil and braise the shanks in the oven until the meat is tender and pulling away from the bones, about 2 hours.
In a deep-sided medium skillet, toast the barley over moderate heat, stirring constantly, until golden brown, about 7 minutes. Add 4 1/2 cups of water, season with salt and bring to a boil. Cover, reduce the heat to moderately low and simmer until the barley is tender and all the water has been absorbed, about 40 minutes. Keep warm.
Transfer the lamb shanks to a platter. Cover with foil and keep warm. Squeeze the garlic cloves from the heads and add to the sauce in the roasting pan, or reserve them for another use. Stir the kale into the sauce until wilted, then strain the sauce into a large nonreactive saucepan; cover the vegetables in the strainer to keep them warm.
Boil the sauce over high heat until reduced to about 41/2 cups; set aside 3/4 cup. Stir the vegetables and barley into the sauce in the saucepan and season with salt and pepper.
Spoon the barley and kale ragout onto 6 large plates and set a lamb shank on top. Spoon the reserved sauce over the meat and garnish with the chopped parsley.