In a small bowls, cover lily buds and tree fungus with boiling water and let stand for 20 minutes.
In a saucepan, bring chicken broth to a boil. Add the vinegar, soy sauce and salt.
In a small bowl, whisk 3 tablespoons of water with corn starch and add to boiling broth while stirring. Let the broth simmer and thicken.
Beat eggs with a pinch of salt. Bring the soup to a full rolling boil. Using a circular motion, pour the eggs into the soup. Wait 5 seconds, then turn off the heat and stir the pot to distribute the eggs throughout the soup.
Add the lily buds, tree ear fungus, bamboo shoots, chicken, tofu and white pepper. Simmer over medium heat for 2 minutes to allow flavors to develop. Season with soy sauce, vinegar, and salt to your taste.
Serve the soup into 4 bowls. Sprinkle with scallions and enjoy.