• Preheat the oven to 325°F
• Season the lamb shanks generously with salt and pepper. Heat the oil in a large Dutch oven, or a brasier pot over medium-high heat. Add 2 of the lamb shanks and brown well on all sides, about 2-3 minutes. Transfer to a plate and set aside and repeat with the remaining 2 lamb shanks.
• In the same pot add the onion, celery, carrot, fennel, garlic, thyme, rosemary and the bay leaves and cook just until the onions are soft. Return the browned lamb shanks to the pot and add the beef broth and 2 cups of wine. The liquid should nearly cover the shanks, add more broth or water if necessary, and bring the pot to a boil.
• Lower the heat, cover the pot, and transfer it to the oven. Let the lamb braise for 2½ to 3 hours, until the meat is fork-tender and nearly falling off the bone. Once done, carefully lift the shanks out of the pot, set them on a platter, and tent loosely with foil to keep warm.
• Pour the cooking liquid through a fine mesh strainer into a saucepan, pressing down on the vegetables to extract every bit of flavor. Discard the solids, then skim off as much fat as you can from the surface.

  Set the pan over medium-high heat, add the remaining cup of wine and the Worcestershire sauce, and bring it to a boil. Let it simmer until reduced to about 2 cups, 5 to 10 minutes.

For the Sauce:

• Meanwhile, mash the softened butter and flour together in a small dish to form a paste. Once the braising liquid has reduced to about 2 cups, take the pan off the heat and whisk in the butter-flour mixture. Return it to the stove and cook for another 2 to 3 minutes, just until the sauce thickens slightly and the flour is fully cooked.
• Serve the lamb shanks in individual shallow bowls on top of mounds of mashed potatoes and garnished with chopped parsley.
• Transfer the sauce to a serving pitcher or dish to be served over the lamb shanks.