Heat the olive oil in a heavy, metal roasting pan on the cooker over medium-high heat. Toss shanks with flour to coat well; then shake off excess. Sear the shanks in hot oil until well browned on all sides, then remove from pan and set aside.
Add the leek, celery, carrot, onion, and garlic to the roasting pan. Cook until softened and lightly browned, stirring constantly; about 5 minutes.
Season with the bay leaf, peppercorns, thyme and rosemary sprigs. Pour in the red wine and chicken stock, increase heat to high, and bring to a simmer.
Season to taste with sea salt, and place the lamb shanks on top of the vegetables.
Cover the roasting pan tightly with heavy foil, and place into the preheated oven. Bake gently until the meat is tender and falls off of the bone, 2 1/2 to 3 hours. Remove the bay leaf and herb stems before serving.