Remove skin from chicken and discard. Cut breasts in half. Remove and discard bones. Pound chicken breasts lightly with mallet or rolling pin. Combine cornstarch, salt and pepper in small bowl. Gradually blend in water and egg yolks. Pour oil into wok. Heat on high heat until oil reaches 375F. Dip chicken breasts, one at a time, into cornstarch-egg yolk mixture.
Fry breasts, two or three at a time, in hot oil until golden. (5 minutes) Drain breasts on paper towels. Keep warm while cooking remaining chicken. Cut each breast into three or four pieces and arrange on serving plate. Sprinkle with onions.
For sauce, combine remaining ingredients in medium saucepan. Stir until blended. Cook over medium heat, stirring constantly, until sauce boils and thickens. (5 minutes) Pour over chicken.