Preheat the oven to 375 degrees F. Season the shanks all over with salt and pepper. In a heavy-bottomed 6 to 8 quart casserole, heat the olive oil until smoking. Place the shanks in the pan and brown all over, turning to get every surface, 12 to 15 minutes. Remove the shanks and set aside. Reduce the heat to medium, add the carrot, onion, celery and thyme leaves and cook, stirring regularly, until golden brown and slightly softened, 8 to 10 minutes. Add the tomato sauce, chicken stock and wine and bring to a boil. Place shanks back into pan, making sure they are submerged at least halfway. If shanks are not covered halfway, add more stock. Cover the pan with tight-fitting lid of aluminum foil. Place in oven for 2 to 2 1/2 hours and cook until meat is nearly falling off the bone.
Remove the casserole from the oven and let stand 10 minutes before serving with Gremolata.
To Make Tomato Sauce: Saute onion and garlic in olive oil over medium heat for about 10 minutes, or until translucent but not browned. Add thyme and carrot, cook 5 minutes over medium heat and add tomatoes. Bring to boil, lower heat to just bubbling and simmer 30 minutes, stirring occasionally. Season with salt to taste and set aside.
Mix the parsley, pine nuts and lemon zest loosely in a small bowl. Set aside utnil ready to serve.