Braise the Shanks:

1. Pat the beef shanks dry with paper towel. Season the shanks with a generous amount of salt and pepper, then dust with flour. Tie kitchen twine around each of the shanks to ensure they hold together during cooking.
2. In a large heavy-bottomed Dutch oven, heat the oil over medium-high heat. Add the shanks and sear on both sides until well browned. Remove from pot and set aside.
3. Add carrot, fennel, onion and garlic to the pot. Cook, stirring frequently, for about 5 minutes or until onion is translucent and soft. Stir in tomato paste, and continue cooking for 1 minute. Stir in wine, gently scraping the pot to release any browned bits clinging to the bottom. Nestle the reserved shanks and bay leaf into the vegetables, and pour beef stock overtop.
4. Bring the mixture to a boil, then reduce heat to low. Simmer, covered, for about 2 hours, or until the shanks are tender and falling off the bone. Check periodically to make sure the shanks are covered 3/4 of the way up with braising liquid, topping up with water if the liquid level gets too low.

Make the Gremolata:

1. While the shanks are braising, stir together all the gremolata ingredients in a small bowl. Cover and transfer to the refrigerator to allow the flavours to mingle.

Finish and Serve:

1. Once shanks are tender, use a slotted spoon to transfer the meat to a serving platter, leaving the liquid in the pot. Snip off kitchen twine from the shanks, and discard.
2. Increase the heat to medium-high. Bring the braising liquid to a boil and cook, stirring frequently, for about 5 minutes or until reduced to a thick, glossy sauce. Discard the bay leaves. Taste to check the seasoning, and adjust as needed with salt and pepper.
3. To serve, top each shank with a generous amount of the sauce from the pot, and finish with a sprinkling of gremolata.