Preheat smoker to 225ºF for indirect grilling with apple or hickory.
Wipe down the pork of any extra liquid then slather the pork with mustard and molasses, making sure it is covered.
Mix all of the spices in a bowl and then rub liberally over the pork.
Place the pork butt fat side up directly on the grill grate and cook until the internal temperature reaches 195℉-202°F, about 15-20 hours.
Remove pork and let rest for 45 minutes before shredding.
While pork is resting, place all of the BBQ sauce ingredients in a pan over medium heat. Bring to boil and cook until sugar and salt are dissolved. Remove from heat and cool to room temperature. Add to jar and shake well before serving.
Notes
This is one of those recipes where you cook to temperature, not time.
Speaking of temperature, I recommend a good instant read probe thermometer so you can track throughout the smoking process.
If you are short on time, wrap in aluminum foil or butcher paper which will speed up the stall. You'll lose some of the bark though.
If you want some of the juices to make a gravy, smoke the pork in a pan.
Leftovers will last for 3-4 days in the fridge or 3 months in the freezer. Use freezer bags.
To reheat, place the pork that is in the freezer bag in a pot of simmering water (not boiling) for about 20 minutes. This lets the pork keep its juices.