Tip:The secret to braising—low and slow cooking in a little liquid—is to maintain a gentle, even simmer. A cast-iron skillet keeps the temperature steady even when the heat is low, and its size works well for smaller cuts of meat, such as short ribs and the lamb shanks here.
Position a rack in the center of the oven and heat the oven to 325°F.
Heat a 12-inch cast-iron skillet over medium-high heat until very hot, about 2 minutes. Add the oil, swirling the pan to coat the bottom; then add the lamb shanks and cook, turning occasionally with tongs, until browned on all sides, 10 to 12 minutes. Remove the skillet from the heat and transfer the shanks to a plate. Season generously with salt and pepper.
Cook the onion in the skillet over medium heat, stirring with a wooden spoon until softened, 2 to 3 minutes. Add the garlic and cook, stirring, for 30 seconds. Stir in the wine, scraping up any browned bits from the bottom of the skillet, and bring the mixture to a boil.
Stir in the cranberries, broth, honey, chipotles, and cumin and cook until the cranberries begin to pop, about 5 minutes. Arrange the shanks in the skillet, cover tightly with an ovenproof domed lid or heavy-duty aluminum foil, and put the skillet on a rimmed baking sheet (to make it easier to transfer without spilling). Transfer to the oven and cook, turning the lamb shanks 2 or 3 times during cooking, until they are fork tender, 2 to 2-1/2 hours.
Transfer the shanks to a medium bowl and cover to keep warm. Skim any fat from the sauce in the skillet and boil over high heat until the liquid lightly coats the back of a spoon, about 8 minutes. Stir in the 1/4 cup cilantro and season to taste with salt and pepper. Return the shanks to the skillet, briefly turning them in the sauce, and serve sprinkled with the remaining 1 Tbs. cilantro.
You can braise the shanks (but don't add the cilantro) up to 3 days ahead. Transfer to a container to cool—storing them in the skillet can give them a metallic flavor and can degrade the pan’s seasoning. Cover and refrigerate. When ready to serve, slowly reheat, covered, in the cast-iron skillet in the oven. Then add the cilantro, season, and garnish as directed above.