Preheat oven to 300 degrees. Crisp pancetta in a large Dutch oven over medium-low heat, until fat is rendered, about 10 minutes. Transfer to a plate using a slotted spoon.
Add onions to Dutch oven. Cook over medium-high heat, stirring occasionally, until caramelized, about 25 minutes. Transfer to plate using slotted spoon.
Season pork with salt and pepper. Add oil to Dutch oven, and sear pork, fat side down, until golden, about 5 minutes. Flip, and repeat.
Add garlic and spices to pot. Cook until fragrant, about 1 minute. Add ale, stock, pancetta, and onions; bring to a simmer. Transfer to oven, and braise pork, covered, basting every hour, until meat is falling off the bone, about 4 hours. Shred meat (just what you're using) using 2 forks, and drizzle with warm skimmed jus.
Serving idea: Pile shredded pork on creamy polenta. Drizzle with jus.
For leftovers: Cut away and reserve skin if making potatoes. Refrigerate pork in jus with onions overnight; skim fat from top (reserve if making potatoes). Reheat pork in oven, and shred just before using. You'll need shredded meat and skimmed jus for all three recipes.