Preheat oven to 225°. Wrap the bottom of a broiler pan with heavy duty foil. Alternately, cover a sheet pan with heavy duty foil and top with a baking rack. Spray top of broiler pan or baking rack with cooking spray.
Rub the butt on all sides thickly with BBQ rub. I use nearly a cup of rub for a 6 lb. butt.
Put the pork fat cap up on the prepared pan/rack, and cook uncovered for about 2 hours per pound.
Remove the pork from the oven and tent loosely with foil. Allow to rest for about a hour before pulling.
Shred pork with two forks or BBQ claws. Do not sauce meat until serving time. Refigerate pulled pork in zipper bags or foil packets and reheat covered in foil. Pulled pork freezes well. To freeze, wrap tightly in a foil packet and place in a freezer zip top bag, squeezing all the air out. To reheat, thaw in the fridge and reheat in the foil at 350° until hot.