Classic Pulled Pork Sandwich

Name: Classic Pulled Pork Sandwich
Ingredients: 2 Tbs. canola oil or vegetable oil; 3 to 4 lb. (1.5 to 2 kg) boneless pork shoulder, cut into 3 equal pieces; 1 yellow onion, finely chopped; 3/4 cup (6 fl. oz./180 ml) cider vinegar; 1 cup (8 fl. oz./250 ml) water; 3/4 cup (6 oz./185 g) ketchup; 1/3 cup (2 1/2 oz./75 g) firmly packed light brown sugar; 1/4 cup (2.75 oz./85 g) light molasses; 1 Tbs. Worcestershire sauce; 1 to 2 tsp. red pepper flakes; 1 tsp. dry mustard; Kosher salt and freshly ground black pepper