4 cups chicken stock (or vegetable stock if you want this to be vegetarian)
light soy sauce
3 tbsp white vinegar
1 tsp ground white pepper
3 oz firm tofu, cut into 2- by 1/4- by 1/4-inch strips
1/2 oz dried wood ear mushrooms, soaked in hot water to rehydrate, and sliced into 1/4-inch ribbons
4 small dried shiitake mushrooms, soaked in hot water to rehydrate, and sliced into 1/4-inch ribbons
2 tbsp cornstarch, dissolved in 2 tbsp cool water
2 large eggs, lightly beaten
1 scallion, white and green parts, thinly sliced on the bias, for garnish
2 tbsp cilantro, finely chopped, for garnish
Combine stock, 3 tbsp light soy sauce (or to taste), vinegar and white pepper in a large pot (we used our Le Creuset like we always do). Add tofu and mushrooms. Bring to a boil over high heat. Reduce the heat to medium. Add the cornstarch slurry slowly into the soup, stirring constantly until the soup has thickened and returned to a boil, about 2 minutes.
Moving in a circular motion around the pot, pour the beaten egg into the soup through the tines of a fork (or a pair of chopsticks) to help it flow in a slow steady stream. You want the egg to form wispy strands, not a large lumpy mass. Gently stir in one direction to integrate the egg into the soup.
Remove from heat. Taste and adjust seasonings as necessary. Ladle soup into individual bowls, drizzle with sesame oil and garnish with scallions and cilantro.