Coat the pork
butt with the mustard. Apply the spice rub all over the pork butt, creating a paste with the mustard
. Place the pork, fat side up, in a preheated 225 to 250 degree F smoker for 10 1/2 hours, or until the internal temperature reaches 190 to 200 degrees F. During the smoking process, leave the smoker closed for the first 2 hours and then spray the pork with a small amount of apple juice or cider every 2 hours thereafter.
Remove pork butt from the smoker and let rest for at least 15 minutes before pulling apart.