Cut ham into 1/4 inch strips; cut strips crosswise into 1/4 inch pieces. Slice celery. Coarsely chop water chestnuts and onion. Set asideCombine broth, cornstarch, soy sauce, ginger, and sugar in a small bowl; stir intil smooth. Set aside.Heat the wok over medium high heat 1 minute or until hot. Drizzle 1 tablespoon oil into the wok and heat 30 seconds. Add ham, celery, water chestnuts, and onion; stir fry about 2 minutes or until ham is lightly browned. Remove ham mixture to medium size bowl. Beat eggs into ham mixture until well mixed.Heat the wok over medium high heat 1 minute. Drizzle 1 tablespoon of oil into the wok and heat 30 seconds. Ladle about 1/4 cup egg mixture into the wok and fry until underside is set and lightly browned. Turn egg foo yung over and fry the other side just until set. Move fried egg foo yung to one side of the wok. Repeat with remaining egg mixture, adding more oil as needed.Transfer egg foo yung to a serving plate and keep warm. Stir cornstarch mixture until smooth and pour into the wok. Cook and stir until sauce boils and thickens. Spoon sauce over egg foo yung.