1 teaspoon white peppercorns or ground white pepper
1 teaspoon coriander seeds or ground coriander
1 packed tablespoon light or dark brown sugar
1 1/2 teaspoons ground turmeric
5 large cloves garlic, roughly chopped
3 tablespoons roughly chopped cilantro stems
1 1/2 tablespoons fish sauce
1 tablespoon oyster sauce
1 1/3 to 1 1/2 pounds (600 to 675g) boneless chicken thighs (with or without skin)
1 lime, quartered (optional)
Grind the peppercorns and coriander seeds in a small food processor to a coarse texture. Add the sugar to grind it a little finer. Visible bits remaining are okay. Add the turmeric, garlic, cilantro, fish sauce, and oyster sauce. Process into a relatively smooth marinade.
Transfer to a bowl. Add the chicken and use your fingers to rub the marinade into the chicken, getting some under the skin if you kept it on the chicken. Cover and refrigerate for 1 to 2 hours.
About 30 minutes before heating, remove the chicken from the fridge and let sit at room temperature to remove the chill.
Heat a gas grill to medium-high or light a charcoal fire, leaving one side free of coals. The grill is ready when you can hold your hand 6 inches (15 cm) over the grill for 4 to 5 seconds.
Cook the chicken for 12 to 15 minutes, turning frequently, until cooked through. Check for doneness by nicking with the tip of a knife. Transfer to a plate and serve with lime wedges.