Preheat your smoker to 250°F.
Spatchcock the chicken as per instructions above.
Season the chicken all over with the barbecue poultry rub, being sure to get underneath the legs and wings.
Place the chicken directly on the grates with the breasts facing up.
For the baste, put the butter and barbecue rub in a small pot. Place the pot on the grates of your smoker next to the chicken so the butter melts. Give it a good stir to combine.
After the chicken has been cooking for 30 minutes, baste the chicken with the butter mixture every 15 minutes.
Around the 1 hour mark, check the internal temperature of the thickest part of the breast, when it reaches 140°F, increase the temperature of the smoker to 350°F and remove the butter pot from the grill.
Let the chicken continue to cook for another 20 to 30 minutes, or until the internal temperature of the breast reaches 165°F.
Remove the chicken from the grill and let it rest for 15 minutes, then slice in and enjoy!