First, prepare the chicken:Remove the backbone from the chicken by cutting down either side of the backbone with chicken shears or a boning knife. You can save the backbone for future use (freeze for use in broth for example). On a cutting board, press the bird flat, flattening the bird so all the skin is facing up. Pat the bird dry all over using paper towels, dispose of the towels.
Place the bird skin side down, sprinkle the cut side (with no skin), with ½ teaspoon kosher salt, flip the bird skin side up, rub the skin with the olive oil and and sprinkle with an additional ½ teaspoon kosher salt.
Place the chicken skin-side down on a hot grill and cook for 10 minutes to fully brown the skin. Then, turn the chicken over – the easiest way to do this with a spatchcocked chicken is to grip the drumstick bones with tongs or with BBQ gloves and lift and flip the bird over. Reduce the heat to medium and cook for 30 minutes.
While the chicken is cooking, make the BBQ sauce (you can also make this in advance): Whisk together ingredients and cook on low heat for 20 mins (a low bubbling simmer).
Back at the grill, turn the chicken back over so the skin is facing down and brush the bone side liberally with the BBQ sauce. Turn it over and brush the skin side liberally with the BBQ sauce. Continue cooking bone side down for 10 minutes and then flip and cook skin side down for 10 minutes. The BBQ sauce should become glossy and crisp on the skin of the chicken as the honey caramelizes. Check the temperature of the whole chicken by inserting a thermometer into the joint between the drum and the thigh – the temperature in the joint should reach 155-160 degrees.