Gather all ingredients.
Prepare the battered chicken: Sift flour, 2 tablespoons cornstarch, baking soda, and baking powder into a bowl. Pour in low-sodium soy sauce, sherry, 2 tablespoons water, vegetable oil, and dash sesame oil; stir until smooth. Stir in chicken until coated with the batter, then cover, and refrigerate for 20 minutes.
Meanwhile, make the sauce: Bring chicken broth, sugar, vinegar, dark soy sauce, sesame oil, chile paste, and garlic to a boil in a saucepan over high heat. Dissolve ¼ cup cornstarch into ½ cup water, and stir into boiling sauce. Simmer until the sauce thickens and turns clear, about 2 minutes. Reduce heat to low, and keep sauce warm.
Heat olive oil in a deep fryer or large saucepan to 375 degrees F (190 degrees C).
Carefully drop in battered chicken pieces, a few at a time, and fry until they turn golden brown and float to the top of the oil, 3 to 4 minutes. Drain on a paper towel-lined plate.
To serve, place fried chicken pieces onto a serving platter, and pour the hot sauce overtop. Sprinkle with toasted sesame seeds to garnish.