Trim the pork butt’s fat cap and place in a large metal roasting pan. Coat the entire pork butt in yellow mustard and season heavily with seasoning of your choice. ( I would recommend something without a lot of salt, because pork tends to be a little bit salty naturally). Cover with foil and let sit in the refrigerator for at least 24 hours.
Prepare your grill to cook at 250 degrees. (We are egg heads around here and used hickory and applewood and placed the plate setter feet up. )
Cook the pork butt until the internal temperature reaches 200 degrees, about 11 hours.
Next, wrap the cooked pork butt in foil. Then wrap in towel and place in a cooler to rest for another 1 1/2 hours.
Meanwhile, make the sauce. In a small saucepan, combine the apple juice, apple cider vinegar, and 2 tablespoons seasoning. Cook over medium heat until the seasoning is dissolved.
Remove the pork butt from the cooler, towel, and foil, and place in a large pan. Remove the bone and shred the meat. Pour the sauce over the meat. Mix well to cover.
Cover with foil if not eating immediately and place in a warm oven until ready to serve. (If you can wait that long!!)