Take the pork butt out of the refrigerator 1 hour before smoking.
Preheat smoker to 225° F. Fill the hopper with your preferred pellets. I use apple wood.
Rub the pork with the mustard and sprinkle on the dry rub.
Place the pork butt into the aluminum pan, fat side up. Insert a digital thermometer into the thickest part of the meat.
Place the pan on the smoker and smoke, without opening the lid, until the meat reaches 145° F.
Pour the apple cider vinegar into the pan and continue smoking until the pork reaches 165° F.
Remove the pork from the smoker and wrap it in butcher paper. Return the pork to the smoker until the meat reaches between 190-202° F (lower for firmer meat, higher for softer meat).
Remove the pork from the smoker and let it rest at room temperature for 40 minutes before shredding.