To season the chicken, in a bowl, combine the chicken and salt and mix until absorbed. Add the white pepper and rice wine and mix well.
To make the batter, in a large bowl, whisk together the cornstarch, baking soda, baking powder, egg, cooking oil, and water until smooth. Add the chicken and coat evenly in the batter.
To prepare the sauce, in a bowl, combine the soy sauce, hoisin sauce, rice vinegar, ketchup, brown sugar, chili oil, and chicken stock and stir until blended. In a separate small bowl, mix the cornstarch and water to form a slurry.
To fry the chicken, in a pot over high heat, heat the cooking oil to 350°F (177°C). Add the battered chicken in batches and fry for about 5 minutes until golden and cooked through. Increase the oil temperature to 375°F (191°C), then return the chicken and fry for 1 minute more until crisp. Transfer to a rack to drain.
To finish the dish, in a wok over medium heat, add the cooking oil. Add the scallions, garlic, and dried chilies and stir-fry for about 10 seconds until fragrant. Pour in the sauce and bring to a simmer. Stir the slurry and pour it in, cooking until the sauce thickens and becomes glossy. Add the fried chicken and toss until evenly coated.
Serve immediately with steamed rice and bok choy.