Transfer the chicken to a medium bowl. Add the soy sauce, garlic powder, five spice, white pepper, and salt and mix until evenly coated. Cover and refrigerate for 1 hour.
In a separate medium bowl, combine the cornstarch and coarse sweet potato flour.
Add the chicken to the flour mixture and toss to coat.
In a deep pot, heat 3 inches of oil over medium heat until the temperature reaches 350°F (150°C). Set a wire rack over a baking sheet.
While the oil is heating, make the spice mix: In a small bowl, stir together the white pepper, salt, five spice, and cayenne.
Drop a handful of Thai basil into the hot oil. Fry for 30 seconds, until starting to crisp. Remove from the hot oil with a slotted spoon and transfer to the wire rack.
Working in batches to avoid overcrowding the pot, fry the chicken in the hot oil for 3–5 minutes, until golden brown and crispy. Transfer to the wire rack to drain.
Transfer the chicken and crispy Thai basil to a large bowl. Sprinkle with the spice mix and gently toss to combine.