Make sure the pork butt is at room temperature and even coat with the seasoning rub mixture. 

Slice the onions and place them into the bottom of a large, high-walled aluminum pan. I used a 13 1/2" x 9" pan. Place the prepared seasoned pork butt into the pan on top of the onions. 

Fill the hopper of the Masterbuilt 800 Gravity Series with your favorite lump charcoal and light. I used the Masterbuilt Lump Premium Hardwood Charcoal.

Turn on the power, and plug the meat thermometer  into one of four ports. Now, push the pointed end of the meat thermometer into the middle of the boneless pork butt.  If you are smoking a bone-in pork butt, make sure the meat thermometer is inserted into the thickest part of the meat but not touching the bone. If the thermometer is touching the bone, it will give a false reading.

Turn on the Masterbuilt grill, adjust the temperature to 190°F, and set the timer for 12 hours. 

Once the temp is at 190°F, place the pan containing the pork butt into the smoker and close the lid. During the 12-hour smoke, you will need to refill the hopper with additional lump charcoal one additional time. 

After the 12-hour smoke, adjust the temperature to 250°F and continue to cook until you get an internal temperature of 105°F.

Remove the pork from the grill and allow it to rest for 15 minutes. Use two forks, or a meat shredder, to pull apart the pork. Add barbecue a little at a time until you get the desired amount.

Serve on toasted buns with coleslaw. Enjoy!