How to Make It
In a small bowl, cover the lily buds with boiling water and let stand until softened, about 10 minutes. In another small bowl, cover the dried wood ear mushrooms with boiling water and let stand until softened, about 20 to 30 minutes. Rinse and coarsely chop.
In a large pot, heat the oil over moderately high heat. Add the garlic, scallions and ginger and cook, stirring, for 1 minute.
Add the vegetable broth and bring to a simmer. Measure out 1/4 cup of the broth and set aside in a small bowl. Add the lily buds, mushrooms, tofu, bamboo shoots, vinegar, soy sauce, sesame oil, pepper and sugar to the pot. Return the soup to a simmer.
Stir the cornstarch into the reserved 1/4 cup of broth, then drizzle the mixture into the soup, stirring gently until slightly thickened, about 3 to 4 minutes.
Taste and add more of the vinegar and soy sauce if desired. Divide into bowls and garnish with the scallions. Serve with chili oil.
Lily buds, wood ear mushrooms, and Chinese black vinegar are available at Asian grocery stores.