Bring Stock To A Boil, Add Meat And All The Mushrooms, Cover, Simmer For 15 Minutes. Add Pepper, Vinegar, Soy Sauce, And Sherry. Simmer For 5 Minutes. Mix Water And Cornstarch Into Paste And Add To Pot. Slowly Add Egg, Stirring Gently. Sprinkle With Sesame Oil And Scallions.