Whisk together flour, cornstarch, baking soda, and baking powder into a bowl. Pour in 2 tablespoons soy sauce, sherry, 2 tablespoons water, 1 teaspoon vegetable oil, and a dash of sesame oil and mix until smooth. Fold in chicken until coated with the batter, then cover, and refrigerate for 20 minutes.
In a medium saucepan, bring chicken broth, sugar, vinegar, dark soy sauce, sesame oil, chile paste, and garlic to a simmer over high heat. Dissolve ¼ cup cornstarch into ½ cup of water, and stir into boiling sauce. Simmer until the sauce thickens. Reduce heat to low, and keep sauce warm.
Heat oil in a deep fryer or large saucepan to a temperature of 375 degrees F (190 degrees C).
Drop in half the battered chicken pieces, and fry until golden brown, 3 to 4 minutes. Remove chicken to a paper towel covered plate and repeat with the remaining chicken. Toss fried chicken pieces in the hot sauce. Sprinkle with toasted sesame seeds to garnish. Serve over hot cooked rice.