Sear the Lamb Shanks: Warm the olive oil in a large, heavy-bottomed pot or Dutch oven over medium-high heat. Season the lamb shanks generously with salt and pepper. Add them to the pot in batches to avoid overcrowding, searing each piece until it develops a deep, golden-brown crust on all sides. Once browned, transfer the lamb shanks to a plate and set aside.
Sauté Aromatics and Vegetables: Into the same pot, add the unpeeled garlic cloves, chopped celery, half of the chopped carrots, and the onion. Cook over medium heat, stirring occasionally, until the vegetables become soft and lightly caramelized, about 10 minutes. This step builds the stew’s flavor base.
Add Tomato Paste and Red Wine: Stir in the tomato paste and cook for 2 minutes, allowing it to darken slightly. Pour in the red wine and raise the heat to high, letting the mixture boil until the wine reduces and thickens into a syrupy consistency, roughly 5 minutes. This intensifies the stew’s richness.
Braise the Lamb: Return the seared lamb shanks to the pot. Add the chicken stock and orange zest strips, then bring everything to a gentle simmer. Cover the pot with a tight-fitting lid, lower the heat, and let the stew cook slowly for about 3 hours, or until the meat is incredibly tender and falling off the bone. Turn the shanks occasionally for even cooking.
Roast the Root Vegetables: Preheat your oven to 350°F (175°C). Toss the rutabaga, turnip, parsnips, and the remaining quartered carrots in a baking dish with a drizzle of olive oil, salt, and pepper. Roast in the oven for about 60 minutes, stirring every 15–20 minutes, until the vegetables are tender and golden brown around the edges.
Prepare the Gremolata: In a small bowl, combine the minced garlic, chopped parsley, and grated lemon zest. Set this fresh, zesty garnish aside to brighten the stew just before serving.
Strain and Finish the Sauce: Carefully remove the lamb shanks from the pot and place on a plate. Pour the stew liquid and vegetables through a coarse sieve or strainer into a bowl, pressing down to extract all the flavorful juices. Discard the vegetable solids and skim any excess fat off the sauce. Return the strained sauce to the pot, season with salt and pepper as needed, and bring to a boil.
Combine Meat and Vegetables: Pull the tender lamb meat from the bones and add it back to the pot along with the roasted root vegetables. Warm everything through over medium heat, stirring gently so the meat and vegetables are coated in the rich sauce.
Serve and Garnish: Ladle the stew into bowls and sprinkle each serving with a generous spoonful of gremolata. This fresh herb topping adds a vibrant contrast to the rich, slow-cooked flavors.