Sift flour, 2 tablespoons cornstarch, baking soda, and baking powder in a bowl. Pour soy sauce, sherry, 2 tablespoons water, vegetable oil, and a dash of sesame oil and stir until smooth.
Stir in chicken until coated with the batter, then cover, and refrigerate for 20 minutes.
Meanwhile, 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 of water, and stir into boiling sauce. Simmer until the sauce thickens and turns clears. Reduce heat to low, and keep sauce warm.
Heat olive oil in a deep fryer or large saucepan to a temperature of 375 degrees F (190 degrees C).
Drop in the 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.
Place fried chicken pieces onto a serving platter, and pour the hot sauce overtop. Sprinkle with toasted sesame seeds to garnish.