To marinate the chicken, in a bowl, combine the chicken with salt and mix until absorbed. Add the white pepper and rice wine and mix well. In a small bowl, combine the cornstarch and water to form a slurry, then add it, along with the egg white, to the chicken. Mix thoroughly and let marinate while preparing the remaining ingredients.
To make the sauce, in a bowl, mix together the soy sauce, oyster sauce, ketchup, sugar, and chicken stock until combined.
To make the batter, in a large bowl, whisk together the cornstarch, baking soda, baking powder, salt, egg, cooking oil, and water until smooth. Add the marinated chicken and coat evenly.
To fry the chicken, in a pot over high heat, add the cooking oil and heat to 350°F (177°C). Fry the chicken in batches for about 5 minutes until golden brown. Remove and drain. Increase the oil temperature to 375°F (191°C), return the chicken, and fry for 1 minute more until extra crispy. Remove and drain well.
To finish the dish, in a pan over medium heat, pour in the sauce and bring to a simmer. Stir the cornstarch and water slurry, then pour it into the sauce and cook until thickened and glossy. Add the roasted sesame seeds and stir. Add the fried chicken and toss until evenly coated. Garnish with scallions and serve immediately.