What's the key to cooking pork shoulder and having it come out juicy every time? Keep it slow and low. If you take your time to cook the meat gently, it will just fall right off the bone.
Place chilies in medium bowl. Add enough boiling water to cover, and set a small plate or bowl on top of peppers to keep them submerged. Let soak until softened, about 30 minutes. Drain chilies, reserving 1 cup soaking liquid.2.
Preheat oven to 350 degrees. Place chilies, sugar, lime juice and 1/4 cup reserved soaking liquid in a blender. Puree the mixture, adding more soaking liquid as needed to form a smooth paste.3.
Season the pork shoulder generously with salt and spread the chile paste over pork (the pork can be rubbed 1 to 2 days ahead. Cover and chill. Let it come to room temperature before continuing.)4.
Heat oil in a large, heavy pot over medium heat. Add the onion, garlic, bay leaves, oregano, coriander, cumin and allspice. Cook, stirring often, until onion is soft, about 8 minutes. Add the beer and bring to a boil. Add pork to pot, cover and transfer to the oven.5.
Braise pork, basting occasionally with pan juices, until very tender, about 2 1/2 to 3 hours.