If your pork belly has the skin on, remove it with a sharp knife.
Slice the slab of pork belly in half to create two smaller portions. This will help reduce cooking time and ensure it cooks evenly.
Coat the pork belly on all sides with the yellow mustard as a binder.
Mix together the Kosher salt and black pepper, then use that mixture to season the pork belly generously on all sides.
Place the slabs of pork belly directly on the grates of the smoker with the fat cap facing down.
Add the apple cider vinegar to a spritz bottle and spritz the pork belly every hour.
Let it smoke for 2-½ to 3 hours until it reaches an internal temperature of 170°F and the bark is firm.
Lay out a sheet of butcher paper and moisten the paper with the spritz bottle.
Place the pork belly on the butcher paper and wrap it tightly. Place it back on the smoker for an additional 1 to 1-½ hours until it reaches an internal temperature of 195°F.
Remove from the smoker and let rest for 30 minutes before slicing.