Pull the shoulder roast out of the fridge 3 hours before cooking to bring it to room temperature. Pat the roast dry and season generously with salt and pepper.

Heat oven to 350ºF (177ºC).

In a Dutch oven or roasting pan, combine the onion, carrots, fennel bulb, garlic, rosemary, thyme, peppercorns, allspice berries, chicken broth, and red wine.

Set the roast, fat side up, in the Dutch oven or roasting pan over the vegetables and cooking liquid when it is at room temperature. Cook in the oven uncovered for 2 hours. Turn the shoulder and cook for another 30 minutes. Turn again and cook for another 30 minutes. Continue to turn the lamb every 20 minutes or so until you can easily pull the meat apart. If you are using two small roasts, your cooking time will be shorter than if you are working with one large roast.

Ensure there is always at least 3/4 of an inch of liquid in the bottom of the pan. Add more broth or water if it seems low. Once the lamb is tender, tent it with foil and let it rest for 15 minutes before carving.

Add all of the pan juices and vegetables to a bowl and strain off the fat. If you can, remove the peppercorns and allspice berries; if not, you can strain them out at the end. Using an immersion blender, purée the vegetables in the pan juice (or use a regular blender) and pour the mixture through a strainer for a silky smooth gravy. If the gravy seems too thick, simply add hot water a little at a time until it reaches a good consistency.

Depending on your roast, you should have a good collection of slices as well as fall-apart meat. Serve on a rimmed cutting board or platter, with the boat of gravy on the side.