Prep the dried mushrooms: Place the shiitake and wood ear mushrooms in separate bowls and cover them with hot water. Let these two ingredients soak for roughly 1 hour or until they are fully rehydrated. Once that’s done remove the mushrooms from the water and slice them into thin strips.
Make the broth base: Bring the 2 quarts of chicken stock to a light boil in a large pot. Add the sugar, salt, both soy sauces, and sesame oil. Stir everything together and let it simmer for a couple of minutes.
Add the mushrooms to the pot and let everything simmer for another couple of minutes. Then add in the sliced tofu along with the julienned bamboo shoots and stir everything together. Let the soup come back to a low simmer.
Thicken with corn starch: whisk together the ⅓ cup of corn starch with a ⅓ cup of water in a small bowl or cup until there are no lumps. Slowly pour half of this corn starch slurry into the soup while simultaneously stirring the soup with a spoon. At this point, the soup should start to thicken up. If the consistency is thick enough for your liking then don’t add the remaining corn starch slurry. However, if you prefer your soup to be of a thicker consistency then add more of the remaining corn starch slurry.
Stir in the egg: Make sure that the soup is at a simmer. Then use either a ladle or a wooden spoon to stir the soup in a circular motion. If you don’t do this then the egg will form large clumps. Keep stirring the soup in this manner and then slowly drizzle the beaten egg into the soup.
Add the ground white pepper and vinegar to the soup, and stir to incorporate them into the broth.
Adjust the soup to your personal preference: Use a small spoon to taste the soup. If it’s not sour enough to your liking then add in a small splash of vinegar. If you want it to be spicier then add some more ground white pepper. And lastly, add in some salt if you feel like it needs it. Just keep adding in small amounts of each ingredient, and tasting the soup until it is exactly how you like it.
Ladle the hot and sour soup into individual bowls and garnish with chopped green onions and cilantro. Enjoy!