Step 1Heat the oven to 350 degrees.
Step 2Season the roast liberally with salt and pepper. Brown the meat in the oil in a large roasting pan over medium-high heat, about 4 minutes a side.
Step 3Remove the pan from the heat and place the roast on a platter. Add the Sherry to the pan. Return the pan to medium-high heat and reduce the Sherry to 1 1/2 cups, about 30 minutes.
Step 4Combine the carrots, onion, celery and leeks with the garlic and lay them in the bottom of the roasting pan. Set the roast on top. Add the bay leaf and the chicken stock; the liquid should cover 3/4 of the meat.
Step 5Cover the roast with foil, sealing it around the pan, and cook in the oven until the meat is very tender, 3 hours.
Step 6When the meat is done, remove it from the oven and let it cool in the braising liquid 30 minutes.
Step 7Remove the meat to a warm platter, strain the cooking liquid and discard the vegetables. Skim the fat from the liquid. Reduce the liquid in a large skillet over medium heat to about 3 1/2 cups, 30 to 40 minutes. Reheat the roast and the liquid before serving.