Add the chicken pieces to a medium bowl with the water, soy sauce, white pepper, MSG (if using), salt, garlic powder, onion powder, and sesame oil. Set aside to marinate for 15 minutes.Then add the batter ingredients: the cornstarch, flour, baking soda, and water. Mix thoroughly to coat the chicken.

Make the sauce mixture by combining the chicken stock, sugar, soy sauce, dark soy sauce, rice vinegar, sesame oil, and chili garlic sauce in a bowl.

Heat the frying oil in a small, deep pot to 335°F (170°C). Carefully drop the chicken pieces into the oil in about three batches. The oil temperature will drop when you add the chicken, so adjust the heat to maintain the frying temperature between 325-335°F (163-170°C).

Fry until light golden brown, about 5-6 minutes, and transfer to a wire rack or plate line with paper towels. Let the chicken rest for at least 10 minutes. Once all of the chicken has been fried once and rested, heat the oil again to 335°F and fry the chicken in two batches for 2 to 3 minutes, or until very crispy.

Heat a clean wok over medium heat. Add 2 teaspoons of the frying oil, along with the minced garlic. After 5 seconds, add the sauce mixture and bring to a simmer.

Gradually add the cornstarch slurry to the sauce, stirring constantly, until the sauce is just thick enough to coat a spoon. Add the fried chicken pieces, and toss until they are completely coated and there is no more standing sauce (about 1 minute). Serve, sprinkled with scallions on top!