How to Make It
Preheat the oven to 325°. Season the lamb shanks generously with salt and pepper. Heat the olive oil in a large enameled cast-iron casserole. Working in batches, brown the lamb shanks thoroughly over moderately high heat, turning often, about 3 minutes per side; transfer the shanks to a large bowl.
Pour off any fat from the casserole. Add the carrots and onion and cook, over moderately high heat, stirring occasionally, until browned, about 5 minutes. Add the wine and boil for 5 minutes, using a wooden spatula to scrape up the browned bits from the bottom of the casserole.
Return the lamb to the casserole. Add the tomatoes, chicken stock, 20 whole garlic cloves, the bay leaves and cinnamon sticks. Tie the parsley sprigs with string and add them to the casserole. Bring to a boil and skim, then cover and cook in the preheated oven for 1 1/2 to 2 hours, or until the lamb is very tender. Remove the casserole from the oven.
Transfer the lamb shanks to a large bowl and cover with foil. Pick out and discard the cinnamon sticks, bay leaves and parsley. Let the cooking liquid stand for 5 minutes, then skim off the fat. Working in batches, puree the cooking liquid and vegetables in a blender. Strain the sauce back into the casserole through a coarse sieve. Boil the sauce until reduced by half, stirring frequently, about 30 minutes. Season with salt and pepper and return the lamb shanks to the sauce.
Bring the shanks to a simmer. In a small bowl, combine the minced garlic with the minced parsley and tangerine zest. Set a lamb shank on each plate. Spoon the sauce over the meat, sprinkle with the gremolata and serve.