Pulled Pork Sandwich

1 medium onion, chopped
½ cup ketchup
1/3 cup cider vinegar
¼ cup packed brown sugar
¼ cup tomato paste
2 T. paprika
2 T. Worcestershire sauce
2 T. yellow mustard
1 1/2 t. salt
1 1/4 t. ground black pepper
4 pounds pork tenderloin
12 hamburger buns , warmed
Dill pickles and potato chips (optional)

1. In a slow-cooker pot, stir onion, ketchup, vinegar, brown sugar, tomato paste, paprika, Worcestershire, mustard, salt, and pepper until combined. Add pork to sauce mixture and turn to coat well.
2. Cover slow cooker with lid and cook pork mixture on high setting for approximately 4 hours or until pork is very tender or 8 hours on low. Note: Can be cooked in oven, too, until pork is very tender. Cover and cook, turning occasionally to keep moist.
3. With tongs, transfer pork to large bowl. Shred pork and return to slow cooker and toss with sauce to combine.
4. Spoon pork mixture onto bottom of sandwich buns; replace tops of buns. Serve with pickles and potato chips, if you like.