1 Brown the lamb shanks: Heat 2 Tbsp of olive oil in a large Dutch oven on medium high heat.
Season the lamb shanks with salt and pepper, add them to the casserole and brown well on all sides, working in batches if necessary. Transfer the shanks to a plate.
2 Add garlic, celery, carrots, onion: Add the unpeeled garlic cloves, celery, chopped carrots (half of your carrots, the other half are cut lengthwise to be used later in the recipe) and onion to the pan. Cook over medium heat, stirring occasionally, until golden brown, about 10 minutes.
3 Add tomato paste, wine: Add the tomato paste and cook, stirring, about 2 minutes. Add the wine; boil over high heat until the liquid is very syrupy, about 5 minutes.
4 Return shanks to pan, add stock, zest, then simmer: Return the shanks to the pot and add the stock and orange zest. Bring to a simmer. Cover the pan, reduce the heat to low, and braise the shank for 3 hours, or until the meat is falling off the bone tender; turn the shanks from time to time as they cook.
5 Roast root vegetables: Preheat oven to 350°F. Put the root vegetables (turnip, rutabaga, parsnips, and lengthwise-cut carrots) in a large baking pan and toss with enough olive oil to coat. Season with salt and pepper and bake in the oven for about an hour, or until tender.
6 Make gremolata: In a small bowl, mix the minced garlic with the parsley and lemon zest (the "gremolata"). Set aside.
7 Strain sauce: Remove the shanks from the pot and transfer to a plate. Pass the sauce through a coarse strainer, pressing hard on the vegetables. Discard the vegetable pulp. Skim the fat from the surface of the sauce.
8 Combine sauce, lamb meat, root vegetables: Return the sauce to the pan, season with salt and pepper and bring to a boil over moderately high heat. Separate the lamb meat from the bones. Add the lamb meat and root vegetables; simmer just until warmed through.
Garnish with the gremolata and serve.