In a large bowl, combine the chicken pieces, pinch of salt, white pepper, and rice wine. Mix well and let it marinate while you prepare the other ingredients.
In a separate large mixing bowl, whisk together the cornstarch, baking soda, baking powder, egg, 1 tablespoon cooking oil, and 3/4 cup water until smooth. Add the marinated chicken to the batter and coat thoroughly.
In a small bowl, whisk together the soy sauce, hoisin sauce, rice vinegar, ketchup, brown sugar, chili oil, and chicken stock. In another small cup, mix the 1 tablespoon cornstarch with 3 tablespoons water to make a slurry.
Heat 4 cups of oil in a pot to 350°F (175°C). Carefully add chicken pieces in batches to avoid overcrowding. Fry for about 5 minutes until light golden. Remove and drain on a wire rack.
Increase the oil temperature to 375°F (190°C). Return the chicken to the oil and flash fry for 1 minute until deep golden brown and super crispy. Remove and set aside.
In a wok or large pan over medium heat, add 1 tablespoon oil. Stir-fry the scallion whites, minced garlic, and dried red chilies for about 10 seconds until fragrant.
Pour in the sauce mixture and bring to a simmer. Stir the cornstarch slurry once more and add it to the simmering sauce. Stir continuously until the sauce thickens and becomes glossy.
Add the double-fried chicken to the wok. Toss quickly to coat every piece evenly in the sauce. Serve immediately with steamed rice.