Place the chicken breast side down on a clean chopping board. Use a sharp boning knife or poultry shears to cut along both sides of the backbone towards the legs.
Trim any excess fat or skin from around the leg end of the chicken.
Flip the chicken over and press down firmly with the palms of your hand so that the meat is flat and spread out.
Pat the chicken dry with paper towels.
Sprinkle liberally with kosher salt and leave uncovered for a few hours in the fridge.
Apply barbecue rub evenly over both sides of the chicken.
Set your smoker up for indirect cooking at 300 - 350°F. Add 2-3 chunks of mild smoke wood (apple or cherry are good options).
Place the chicken on the grill, breast side up.
Smoke until the internal temperature of the breast reaches 160°F. Around 1 hour.
Take the chicken off the smoker and spread barbecue sauce evenly over the skin.
Place chicken back on the smoker for about 10 minutes or until the breast reaches 165°F.
Slice the chicken up and serve with your favorite barbecue sides, or pull the meat and use in a sandwich.