Spatchcock your chicken by cutting down the length of the spine on each side with kitchen shears and removing the back. Open the bird, flatten it, and apply pressure to the breast like you’re doing CPR. You’ll hear a couple of pops which will help your bird lie flatter. Trim excess fat from the opening of the neck and the bottom of the thighs and reserve.
Combine the marinade ingredients in a 1-gallon Ziploc bag, then add the chicken, squeezing out all the air before sealing it. Then give your chicken a nice massage. Let it marinate in the refrigerator overnight, or for at least 4 hours.
At least an hour before cook time, remove the chicken from the fridge and allow to come to room temperature. Start your grill, implementing the two-zone method (warm spot, and hot spot), and let it get to roughly 350° F.
Make the basting liquid by steeping all aromatics in the melted butter, then blend and strain. Add the calamansi or lemon juice after it is blended. Set aside.
Remove chicken from marinade, pat dry, and remove any and all loose aromatics from the skin. Apply one coat of the baste with a brush to both sides of the chicken. Then place the chicken, flesh side down, on the warm spot of the grill and close the lid. After 15 minutes come back and baste the skin side. Repeat until the internal temperature of the thighs hits 165° F, roughly 40–45 minutes.
For the last 5–10 minutes, flip the chicken over and place it skin-side down on the hot side of the grill. Baste the flesh side a couple of times before removing. Apply one last sprinkle of salt. Serve alongside chicken fat rice, and enjoy!