Instructions

1. Place a rack in the middle of the oven and heat to 500°F. Line a rimmed baking sheet with aluminum foil.
2. Mix together brown sugar, smoked paprika, chili powder, salt, pepper, oregano, garlic powder, and onion powder in a small bowl to create rub for pork.
3. Dry pork with paper towels, then rub evenly with rub. Keep remaining rub.
4. Place pork on baking sheet and cook until the meat slightly charred on the edges, about 15 minutes.
5. While the meat is in the oven, place onions in a 6-quart or larger slow cooker and sprinkle with reserved rub. Pour in enchilada sauce, stock, and cider vinegar.
6. Using two forks stabbed into the ends of the pork (like handles), carefully transfer the pork into the slow cooker. Cover and cook on low until the meat is soft enough to pull apart with a spoon, at least 12 hours.
7. Transfer the meat to a large plate or bowl and rest until cool enough to handle. Pull the meat apart into large chunks or shred with a fork, discarding any bone, tissue, or large pieces of fat.