In a mortar and pestle (or food processor), pound the garlic, cilantro roots, and white pepper into a paste.
In a large bowl, mix the fish sauce, soy sauce, salt, and the garlic-cilantro paste.
Add the chicken, making sure each piece is well-coated.
Cover and let it marinate for at least 2 hours (overnight is even better for maximum flavor).
Remove the chicken from the marinade, letting the excess drip off.
Dredge each piece in rice flour (or cornstarch), coating it lightly.
Let the coated chicken sit for 10 minutes—this helps the coating stick.
In a deep frying pan or wok, heat about 2 inches of oil to 350°F (175°C).
Test the oil by dropping in a small piece of batter—if it sizzles immediately, it’s ready.
Carefully place the chicken in the hot oil, frying in batches to avoid overcrowding.
Fry for about 6-8 minutes per side, or until golden brown and crispy.
Use a thermometer to check that the internal temperature reaches 165°F (74°C).
Transfer to a wire rack to drain excess oil.
Let the chicken rest for a few minutes before serving.
Serve hot with sweet chili sauce, sticky rice, and fresh cucumber slices.