Prepare the marinade: In a mortar and pestle or food processor, combine garlic, lemongrass, white peppercorns, fish sauce, soy sauce, oyster sauce, palm sugar, and turmeric (if using). Process until a smooth paste forms.

Marinate the chicken: Pat the chicken pieces dry. Make a few shallow slits in the skin of each chicken piece to help the marinade penetrate. Rub the marinade all over the chicken, ensuring it gets under the skin. Place in a bowl, cover, and refrigerate for at least 4 hours, or preferably overnight.

Prepare for grilling: Preheat your grill (charcoal or gas) to medium-high heat. Lightly oil the grill grates to prevent sticking.

Grill the chicken: Place the marinated chicken pieces skin-side down on the hot grill. Grill for 15-20 minutes per side, or until the internal temperature reaches 165°F (74°C) and the skin is crispy and charred in places. Flip occasionally to ensure even cooking and prevent burning.

Rest and serve: Once cooked, remove the chicken from the grill and let it rest for 5-10 minutes before serving. This helps the juices redistribute, keeping the chicken moist.

Serve hot with sticky rice, a fresh salad, and a traditional Thai dipping sauce (Nam Jim Jaew recommended).