Wipe the chicken fillets dry with paper towels and cut into bite-size pieces.
Place the chicken in a bowl. Add the oyster sauce, rice wine, half of the five-spice powder, half of the salt, half of the Sichuan peppercorns and half of the ground white pepper. Mix well.
Add the egg white and two tablespoons tapioca starch, and mix.
Cover the bowl and leave the chicken to marinate in the fridge for 30 minutes.
In a small bowl, stir together the remaining five-spice powder, salt, Sichuan peppercorns and white pepper.
In a wok or frying pan, heat enough cooking oil to reach a depth of at least three inches.
Take the chicken out of the fridge and toss with the remaining tapioca starch (with the baking powder mixed in). Shake off the excess.
Over medium heat (about 300F), fry the chicken for three to four minutes, or just until a crust forms on the surface.
Scoop out the chicken, dump into a strainer and allow to reast for a couple of minutes.
Turn up the heat to high (350F) and fry the chicken a second time for about a minute.
Add the Thai basil leaves to the chicken and continue frying for a minute or until the Thai basil leaves start to turn crisp.
Scoop out the chicken and Thai basil and dump into a clean bowl.
Sprinkle the remaining spice mixture over the chicken and Thai basil, and toss a few times.
Transfer the Taiwanese popcorn chicken to a plate and serve at once.