In A Bowl, Combine The Cornstarch, Broth, Soy Sauce, Peanut Butter, Sugar And Pepper Until Smooth; Set Aside. In A Large Skillet Or Wok, Stir-Fry The Beef, Onion, Celery And Garlic In Oil For 5-8 Minutes Or Until Meat Is No Longer Pink. Stir The Broth Mixture And Add To The Pan. Bring To A Boil; Cook And Stir For 1-2 Minutes Or Until Thickened.