* if soup is not thick enough, add 2 more spoons of cornstarch (mixed into cold water) into the soup
In a small bowl, cover the mushrooms with 1/2 cup of warm water and let them soak for 30 minutes. Discard the water. With a cleaver or knife, cut away and discard the tough stems of the mushrooms, and shred the caps by placing one at a time on a chopping board. Cut them horizontally into paper-thin slices, and then into thin strips.
Drain the pieces of bamboo shoots and bean curd, and rinse them in cold water. Shred them as fine as the mushrooms.
With a cleaver or sharp knife, trim the pork of all fat. Then shred it, too, by slicing the meat as thin as possible and cutting the slices into narrow strips about 1-1/2 to 2 inches long.
Have the above ingredients, stock, salt, soy sauce, pepper, vinegar, cornstarch mixture, egg, sesame seed oil and scallions within easy reach.
TO COOK: Combine in a heavy 3-quart saucepan the stock, salt, soy sauce, mushrooms, bamboo shoots and pork. Bring to a boil over high heat, then immediately reduce the heat to low, cover the pan and simmer for 3 minutes. Drop in the bean curd and the pepper and the vinegar. Bring to a boil again. Give the cornstarch mixture a stir to recombine it and pour it into the soup. Stir for a few seconds until the soup thickens, then slowly pour in the beaten egg, stirring gently all the while. Remove the soup from the heat and ladle it into a tureen or serving bowl. Stir in the sesame seed oil and sprinkle the top with scallions. Serve at once.