Marinate chicken in corn flour, salt, sesame oil, shaoxing wine, dark soy sauce, light soy sauce, and white pepper.
Allow to marinade for at least 30 minutes.
Heat oil in wok on high until hot is simmering.
Add chicken in single layer to sear and brown on all sides.
Remove from heat and transfer chicken from wok to plate.
Leave about 1-2 tbsp oil in wok.
Add szechuan peppercorn in wok and heat over medium heat.
Toast for about a minute then add garlic and ginger.
Stir-fry for another minute then add chilli flakes and dried chillies, then cook for another minute.
Crank the heat up back to high, and add the chicken pieces, sugar, and scallion.
Stir-fry quickly for another minute or 2.