Fire up your electric smoker to 225°F (107°C). Fill the water pan with fresh water and add 1:1 ratio of hickory and applewood to your smoker’s wood tray/box.
Pat pork butt dry with paper towels
Combine all dry rub ingredients in a small bowl. Use a fork to remove any lumps that may appear.
Coat the pork butt in a thin layer of yellow mustard. Apply a generous amount of dry rub seasoning to the pork, covering all sides and working into any creases.
Place pork butt fat-side down on smoker grates. Close smoker door and smoke for 3 hours, until it starts to brown and develop a bark.
Combine spritz ingredients in a spray bottle. Spritz pork every 30 minutes. Smoke until pork internal temperature is 165°F (75°C).
Wrap pork in aluminum foil. Add 2 tablespoons of the spritz solution to the foil package, and sprinkle more BBQ rub across pork. Wrap tightly and smoke for 2-3 hours, or until internal temperature has reached 195°F (90°C).
Remove from smoker. Leave in foil and allow pork to rest for at least 10 minutes before serving.