Prepare the pork butt by trimming off the fat cap and any excess fat on the meat. Slather the pork with yellow mustard. Apply a heavy layer of seasoning on all sides of the meat and allow it to set out for 20-30 minutes or refrigerate overnight.
Preheat your grill or smoker to a temperature of 275°F and place the prepared meat directly on the grill grates.
Place a small foil pan containing apple juice next to the meat inside the grill.
Spritz the pork with apple cider vinegar around every 2 hours or as it begins to appear dry.
Once the meat appears to have a nice outside bark and has an internal temperature of around 160-170°F, remove it from the grill and place it in an aluminum pan to be wrapped.
After removing the pork from the grill and placing it in an aluminum foil pan, apply another layer of seasoning on the meat and top it with a few tablespoons of sliced butter. Use heavy duty aluminum foil and wrap the pork in the pan and place it back on the grill.
Allow the meat to continue to cook until it reaches an internal temperature of 200°F. The total cook time will be around 10-12 hours depending on the size of meat you cook.
Let the pork butt rest 30-60 minutes before pulling it apart and then enjoy.