Trim the excess fat from the pork butt.
Slather the pork butt with yellow mustard, then apply a generous coating of rub.
Wrap the pork butt in plastic wrap and place in the refrigerator overnight.
Prepare the mopping sauce by combining all of the mop sauce ingredients in a lidded container. Shake to combine.
When ready to cook, heat your smoker to 250 degrees. Smoke the pork butt until the bark is set. This typically occurs at roughly an internal temperature of 165-185 degrees, but will depend on the rub.
Once the bark is set, begin mopping the pork butt with the mopping sauce each hour. Increase the mopping frequency to every 30 minutes once you reach 185 degrees.
If using an instant read thermometer, remove the pork butt from the smoker when it is probe tender. If only using an indwelling meat thermometer this is typically between 203-205 degrees. The bone should pull out cleanly from the pork butt at this point. Total cook time is typically 8-10 hours but can vary greatly, so monitor the meat temp.
Wrap the pork but in foil and rest for at least to hours in a cooler filled with towels, a Cambro, or an oven set to about 150-160 degrees.
At the end of the rest, pull the pork apart with forks or with insulated gloves. Combine with any juices left in the foil.
Serve with a side of the vinegar (mopping) sauce and enjoy.