In a small bowl, combine the cornstarch, consomme, soy sauce and sugar until smooth; set aside. In a large skillet or wok, stir-fry beef in batches in hot oil for 2-3 minutes or until no longer pink. Remove and keep warm.
In the same pan, stir-fry onion and celery for 5 minutes. Add mushrooms and green onions; stir-fry 3-4 minutes longer or until vegetables are tender.
Return beef to the pan. Add spinach. Stir cornstarch mixture and add to the pan. Bring to a boil; cook and stir until thickened. Serve with rice if desired. Yield: 6 servings.