In a bowl, mix flour, cornstarch, baking powder, salt, and white pepper to create the batter.
Coat chicken pieces thoroughly in the batter mixture.
Heat oil to 350°F (175°C) in a deep pan or fryer.
Fry chicken pieces until golden brown and cooked through, about 4-5 minutes. Drain on paper towels.
In a separate pan, sauté minced garlic and ginger for 30 seconds until fragrant.
Add soy sauce, sugar, chicken stock, and vinegar to the pan. Bring to a simmer.
Stir in the cornstarch slurry and cook until sauce thickens, about 1-2 minutes.
Add fried chicken to the sauce and toss until well coated.
Garnish with chopped scallions and sesame seeds before serving.