Cut chicken into bite-size pieces; sprinkle with sherry, salt, and pepper. Set aside. Beat egg whites (at room temperature) at high speed of an electric mixer until foamy. Gradually add cornstarch to egg whites, beating until stiff peaks form. Gently fold in chicken. Roll each chicken piece in chopped walnuts; fry in 2 inches of hot oil (350 degrees) until golden brown. Drain on paper towels. Serve chicken with Gingered Plum Sauce. Yields: about 3 dozen appetizers.