Place pepper-coriander root flavor paste in a large bowl and stir in the fish sauce. Place the chicken pieces in the marinade and turn to coat well. Let stand, covered, at room temperature for about 1 hour or in the refrigerator and for as long as 3 hours.
Heat a grill or preheat the broiler. If using a grill, place the chicken pieces 4 to 5 inches from the flame, bone side down, and grill until the bottom side is starting to brown, about 6 to 8 minutes. Then, turn over and cook until golden brown on the other side and the juices run clear when the meat is pierced.
If using a broiler, put the chicken pieces in a lightly oiled broiling pan, bone side up, place 4 to 6 inches from the broiler element, and cook for 8 to 10 minutes, or until the chicken is starting to brown. Turn the pieces over and broil for another 8 minutes, or until the juices run clear.
Transfer the chicken pieces to a platter and serve with dipping sauce and plenty of sticky rice.
Pepper-Coriander Root Flavor Paste:
Place the peppercorns in a mortar with the garlic and pound to a paste. Add the coriander roots and salt and pound to a paste. This will take 5 to 10 minutes; if you have a small blender or other food grinder that can produce a smooth paste, use it instead. Stir in the fish sauce. Will keep in a well-sealed glass jar for up to 4 days.
Yield: 2 to 3 tablespoons paste
Hot and Sweet Dipping Sauce:
Place the vinegar in a small non-reactive saucepan and heat to a boil. Add the sugar, stirring until it has completely dissolved, then lower the heat to medium-low and let simmer for 5 minutes.
Meanwhile, using a mortar and pestle or a bowl and the back of a spoon, pound or mash the garlic and salt to a smooth paste. Stir in the pepper flakes and blend well. Remove the vinegar mixture from the heat and stir in the garlic paste. Let cool to room temperature. Store sealed in a glass jar in the refrigerator for up to 2 days.