Thai-style grilled chicken coated in a marinade flavored with cilantro, white pepper, and fish sauce is one of the tastiest things you'll ever pull off of your grill. There's a reason you can't walk more than a few blocks in Bangkok without catching a whiff of its intense aroma. Here's how to make it in your own backyard.
For the sauce, see this recipe.
Combine garlic, cilantro, sugar, white pepper, coriander, fish sauce, dark soy sauce, and lemongrass (if using) in the bowl of a food processor. Process until a rough paste is formed. Set aside.
Place chicken halves flat on a cutting board. Insert two metal skewers into each chicken, running parallel through the legs and the breasts. Transfer chicken to a casserole dish that just fits them. Rub on all surfaces with marinade. Cover, transfer to refrigerator, and allow to marinate for at least 2 hours and up to over night.
When ready to cook, light one chimney full of charcoal. When all the charcoal is lit and covered with gray ash, pour out and spread the coals evenly over half of coal grate. Alternatively, set half the burners of a gas grill to high heat. Set cooking grate in place, cover gill and allow to preheat for 5 minutes. Clean and oil the grilling grate.
Place chicken skin-side up on cooler side of grill with legs facing towards hotter side. Cover grill with vents on lid open and aligned over the chicken. Open bottom vents of grill. Cook until instant read thermometer inserted into deepest part of breast registers 140°F, about 45 minutes. Carefully flip chicken and place skin-side-down on hotter side of grill with breasts pointed towards cooler side. Cover and cook until skin is crisp and instant read thermometer inserted into deepest part of breast registers 145 to 150°F, about 3 minutes longer (be careful, the skin is very prone to burning). If chicken threatens to burn before temperature is achieved, carefully slide to cooler side of grill, cover, and continue to cook until done. Do not leave the lid off for longer than it takes to check temperature or chicken will burn.
Transfer chicken to a cutting board and allow to rest for 5 minutes. Carve and serve with dipping sauce.