To make slicing the pork chop easier, freeze it for 15 minutes. We prefer the distinctive flavor of Chinese black vinegar; look for it in Asian supermarkets. If you can’t find it, a combination of red wine vinegar and balsamic vinegar approximates its flavor. This soup is very spicy. For a less spicy soup, omit the chili oil altogether or add only 1 teaspoon.
7 ounces extra-firm tofu, drained
4 tablespoons soy sauce
1 teaspoon toasted sesame oil
3 tablespoons plus 11/2 teaspoons cornstarch
1 boneless center-cut pork chop (1/2 inch thick, about 6 ounces), trimmed of fat and cut into 1-inch by 1/8-inch matchsticks
3 tablespoons plus 1 teaspoon cool water
1 large egg
6 cups low-sodium chicken broth
1 cup bamboo shoots (from one 5-ounce can), sliced lengthwise into 1/8-inch-thick strips
4 ounces fresh shiitake mushrooms, stems removed, caps sliced 1/4 inch thick (about 1 cup)
5 tablespoons Chinese black vinegar or 1 tablespoon red wine vinegar plus 1 tablespoon balsamic vinegar (see note)
2 teaspoons chili oil (see note)
1 teaspoon ground white pepper
3 medium scallions, sliced thin
1. Place the tofu in a pie plate and set a heavy plate on top. Weight with 2 heavy cans and let stand at least 15 minutes (the tofu should release about 1/2 cup liquid). Whisk 1 tablespoon soy sauce, sesame oil, and 1 teaspoon cornstarch in medium bowl; toss the pork with the marinade and set aside for at least 10 minutes (but no more than 30 minutes).
2. Combine 3 tablespoons of the cornstarch with 3 tablespoons of the water in a small bowl and mix thoroughly; set aside, leaving the spoon in the bowl. Mix the remaining 1/2 teaspoon cornstarch with the remaining 1 teaspoon water in a small bowl; add the egg and beat with a fork until combined. Set aside.
3. Bring the broth to a boil in a large saucepan over medium-high heat. Reduce the heat to medium-low and add the bamboo shoots and mushrooms and simmer until the mushrooms are just tender, about 5 minutes. While the broth simmers, dice the tofu into 1/2-inch cubes. Add the tofu and pork, including the marinade, to the soup, stirring to separate any pieces of pork that stick together. Continue to simmer until the pork is no longer pink, about 2 minutes.
4. Stir the cornstarch mixture to recombine. Add it to the soup, increase the heat to medium-high, and cook, stirring occasionally, until the soup thickens and turns translucent, about 1 minute. Stir in the vinegar, chili oil, pepper, and remaining 3 tablespoons soy sauce and turn off the heat.
5. Without stirring the soup, use a soupspoon to slowly drizzle very thin streams of the egg mixture into the pot in a circular motion. Let the soup sit 1 minute, then return the saucepan to medium-high heat. Bring the soup to a gentle boil, then immediately remove from the heat. Gently stir the soup once to evenly distribute the egg; ladle into bowls and top with the scallions.