Grind the white peppercorns and coriander seeds into a fine powder using a mortar and pestle or a coffee grinder.

Add the lemongrass and garlic; pound until it forms a fine paste.

Transfer the mixture to a bowl and add the remaining marinade ingredients: soy sauce, fish sauce, black soy sauce, sugar, and water. Stir until the sugar dissolves.

Split the bone-in chicken breast in half and separate the thighs from the drumsticks. Trim any excess skin from the thighs.

Place the chicken pieces in a zip-top bag or a shallow dish. Pour the marinade over the chicken and ensure each piece is well coated. Marinate for at least 2 hours, preferably overnight. Flip the bag or turn the chicken halfway through for even marination.

In a dry skillet, toast raw rice over medium heat until dark brown. Let it cool, then grind it into a powder.

In a bowl, combine tamarind paste, fish sauce, lime juice, and sugar until dissolved. Add chili flakes and shallots. Stir in green onions and cilantro, then gently fold in the toasted rice powder right before serving.

Preheat your grill to medium heat.

Grill the chicken skin-side up, turning every 5 minutes. The cooking time will vary, taking about 18-30 minutes. Check for doneness using a meat thermometer: 160°F for breast, 175°F for thighs/drums. The skin should be beautifully charred and crisp.