Chicken thigh fillets are ideal for cooking Taiwanese popcorn chicken but if you prefer breast meat, feel free to substitute. Just remember that chicken breast meat will dry our faster so a shorter frying time is recommended.
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 wok or frying pan, heat enough cooking oil to reach a depth of at least three inches.
In a small bowl, stir together the remaining five-spice powder, salt, Sichuan peppercorns, white pepper and baking powder.
Take the chicken out of the fridge and toss with the remaining tapioca starch. 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 in a bit of five-spice powder, a few pinches of rock salt and Sichuan peppercorns over the chicken and Thai basil, and toss a few times.
Transfer the Taiwanese popcorn chicken to a plate and serve at once.