Marinate the chicken with egg white, potato starch and cooking wine for about 10 minutes.
Whisk ketchup, sugar, vinegar, salt and water in a small bowl as the sauce for later use.
Heat the oil in a pan over medium-low heat, carefully add in the chicken, deep fry for about 15 minutes until browned and crisp on the surface, fish out the chicken and set aside.
Leave about 1 tablespoon of oil in the pan, turn to medium heat, add in the sauce and cook for about 3 minutes until it starts to thicken, stir occasionally during the cooking process.
Stir in the chicken, stir-fry for about 2-3 minutes, make sure the sauce has evenly coated the chicken.