Place the pork butt on a flat sheet pan, fat side down. With a sharp knife, puncture holes all over the top and sides of the pork. Generously rub the top and sides with the mustard. Generously sprinkle the top and sides with the seasonings.
Flip the pork over and score the fat side with the knife. Generously rub in the mustard followed by the seasonings. Place in the fridge, uncovered, for at least 6 hours, or overnight.
Remove the pork butt from the fridge at least 1 hour before cooking.
Preheat the smoker to 275 degrees F. Place a pan of water either under or on the side of the smoker grate. Add a few chunks of smoking wood (I like to add a few chunks of hickory and cherry to the hardwood lump).
Place the pork on the smoker, fat side up. Shut the lid and smoke for about 3 hours, or until the internal temperature is 165 degrees F.
Remove the pork from the smoker and place on 2 sheets of aluminum foil. Generously spray the pork with the apple cider vinegar. Wrap the pork up tightly with the foil. Place back on the smoker.
Increase the smoker temperature to 300 degrees F. Continue cooking for about 3 hours, or until the internal temperature of the pork is 200 - 205 degrees F.
Remove the pork from the smoker and let rest, covered, for 45 minutes to 1 hour. Remove the foil and shred the pork. Add to hamburger buns and top with bbq sauce, onions, pickles and any additional toppings. Serve warm.
