To butterfly the chicken, you need to remove the backbone. You can do this with poultry shears or a chef's knife. If using poultry shears, turn the chicken, breast side down, on a cutting board and cut from the neck to the tail along both sides of the backbone to release it. If using a chef's knife, turn the chicken, breast side up, on a cutting board. Insert the chef's knife into the body cavity and cut along both sides of the backbone to release it. With the breast side up, press on the breastbone with the heel of your hand to flatten the bird. Cut off the wing tips and discard.

To make the marinade, put the garlic, shallot, lemongrass, ginger, and sugar in a food processor and pulse until very finely chopped. With the motor running, add the soy sauce through the feed tube and puree until the paste is as fine as possible. Transfer to a bowl and whisk in the fish sauce, five-spice powder, and pepper.

Place the flattened chicken in a large baking dish, pour the marinade over it, and turn the bird to coat on both sides. Cover with plastic wrap and refrigerate. Alternatively, you can put the chicken and its marinade in a 1-gallon heavy-duty resealable food storage bag and refrigerate. Marinate for 6 to 8 hours.

Remove the chicken from the refrigerator about 1 hour before you plan to grill. Prepare a moderate charcoal fire for indirect grilling or preheat a gas grill to medium (375°F), leaving one burner unlit for indirect grilling.

Remove the chicken from the marinade, reserving the marinade. Brush the skin side of the chicken with some of the marinade. Place the chicken, skin side down, over indirect heat. Cover the grill and cook until the skin is richly browned and crisp, 15 to 20 minutes. Brush the flesh side of the chicken with the remaining marinade, then turn the chicken, skin side up, cover the grill, and continue grilling over indirect heat until the juices run clear when a thigh is pierced, or an instant-read thermometer inserted in the thickest part of the thigh away from the bone registers 165°F, about 15 minutes longer. Let rest for 10 minutes before carving into serving pieces.