In a bowl, marinate the chicken with ginger root, sherry, 1½ teaspoons of cornstarch, and salt. Refrigerate for half an hour. In another small bowl, mix the chicken broth, soy sauce, vinegar, 2 teaspoons of cornstarch, and sugar together; set aside. In a heavy skillet, heat 2 tablespoons of the oil and stir fry the chicken until it is cooked.