How to Make It
Heat 2 tablespoons of the olive oil in a large enameled cast-iron casserole. Season the lamb shanks with salt and pepper, add them to the casserole and brown well on all sides, about 8 minutes. Transfer the shanks to a plate.
Preheat the oven to 350°. Add the unpeeled garlic cloves, celery, carrots and onion to the casserole and cook over moderate heat, stirring occasionally, until golden brown, about 8 minutes. Add the tomato paste and cook, stirring, until glossy, about 2 minutes. Add the wine and boil over high heat until the liquid is very syrupy, about 15 minutes.
Return the shanks to the casserole and add the stock and orange zest. Bring to a simmer. Cover the casserole and braise the shanks in the oven for about 2 hours, or until the meat is very tender; turn the shanks from time to time as they cook.
Meanwhile, on a large rimmed baking sheet, toss the squash cubes with the remaining 1 tablespoon of olive oil. Season with salt and pepper and bake in the oven (along with the lamb) for about 1 hour, or until tender.
In a small bowl, mix the minced garlic with the parsley and lemon zest. Set the gremolata aside.
Remove the shanks from the oven and transfer to a plate. Pass the sauce through a coarse strainer, pressing hard on the vegetables. Skim the fat from the surface of the sauce.
Return the sauce to the casserole, season with salt and pepper and bring to a boil over moderately high heat. Add the lamb shanks and squash and simmer just until warmed through. Add the cannellini beans, cover and remove from the heat. Let stand for a few minutes to allow the flavors to blend.
Spoon the vegetables and sauce into 2 large shallow bowls and set the lamb shanks on top. Garnish with the gremolata and serve.