Preheat the oven to 400 degrees F. Heat 3 tablespoons of the oil in a large saute pan over medium-high heat. When the oil begins to smoke, carefully place one piece of pork in the saute pan and sear, turning once, until golden. Remove to a plate and repeat with the remaining pieces of pork. Set aside.
Carefully add the beer to the drippings in the pan and cook, scraping up the cooked bits with a wooden spoon, until reduced.
Heat the remaining 5 tablespoons of oil in a large flame-proof roasting pan over medium heat. Add the celery, onions, carrots, garlic and cook, stirring occasionally, until caramelized, 8 to 10 minutes.
Add the pork to the roasting pan. Add the deglazed pan juices and enough chicken stock to cover the pork and vegetables. Add the peppercorns, thyme, bay leaves and 2 generous pinches of salt. Cover the pan with foil and braise for 3 hours. Remove the foil and roast 30 minutes more. This will allow the pork to gain a beautiful color and for the braising liquid to reduce.
Let the pork cool in the braising liquid for 30 minutes to increase tenderness. Remove the pork from the roasting pan and strain the braising liquid. Refrigerate separately until ready to use. The pork can be served sliced or shredded.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.