Partially freeze pork; cut pork into 1x 1 cm strips. Sprinkle meat with 1 tablespoon of the soy sauce. Meanwhile, in three bowls soak lily buds, mushrooms, and tree ears in enough hot water to cover for 30 minutes. Drain lily buds, mushrooms, and tree ears. Cut off and discard tough stem end of lily buds. Slice each lily bud into 3 cm lengths. Thoroughly rinse tree ears under running water; drain well. Cut off and discard stems. Cut mushrooms and tree ears into thin strips. In large saucepan bring chicken broth to boiling; stir in pork, the remaining soy sauce, lily buds, mushrooms, tree ears, rice wine vinegar and pepper. Simmer covered, 10 minutes. Slice tofu into 1 cm wide strips. Add to soup simmer, covered, 3 minutes more. Blend cold water into cornstarch. Stir into soup. Pour egg slowly into hot soup in a thin stream, beating constantly with fork till egg cooks and shreds finely. Cook soup till slightly thickened and bubbly. Remove from heat. Stir in thinly sliced green onion. 6-8 servings