Heat oil in a pot or wok, and then fry the mushrooms for around 30 seconds until slightly soft.
Pour water or stock in along with ginger slices. Bring to boil and simmer for 5-8 minutes.
Turn up the fire and pour the whisked egg in. At the same time, stir the soup with a scoop either quickly or slowly. When the egg flour is formed, turn off the fire. Add sesame oil and pinch of salt, and then combine well.