Soak the mushrooms if using dried: Place the mushrooms in a bowl. Cover shiitake mushrooms and wood ear mushrooms with plenty of boiling water. Place a small plate over the mushrooms to keep them submerged in the water. Let the mushrooms rehydrate for 20-30 minutes until soft. Drain them, trim woody stems off shiitakes, then slice thinly. (Discard or reserve soaking liquid for other use)

Cut the block of tofu horizontally into thin sheets. Cut across the tofu on the short end to create thin strips. Set aside.

Make the soup: Place chicken broth, soy sauce, chilli, and sugar in a large pot over high heat and bring to a simmer.

Add the mushrooms (if you are using dried ones) and chicken and stir with chopsticks or a spoon, to separate the chicken pieces. Cover with a lid and reduce heat to medium so it’s simmering. Cook for 5 minutes.

Add the bamboo shoots, mushrooms (if you are using fresh ones), and tofu into the soup and season with ground white pepper. Simmer covered for 5 minutes.

Thicken the soup Mix the cornstarch with water until the slurry is smooth. While stirring the soup, slowly pour the slurry in (this keeps the soup free of clumps).

When the soup is back at a simmer again and slightly thickened, slowly pour the egg in a thin stream in circles, to create streaks of egg ribbon. Let it cook for another minute and turn off the heat.

Add the vinegar and sesame oil. Stir gently and taste. Adjust seasonings with chili flakes, more vinegar, white pepper or salt as desired.

Garnish with scallions, transfer to bowls, and serve immediately.