6TblsChinese vinegar, apple cider vinegar or rice wine vinegar
2tspdark soy sauce(for coloring purpose)
6dashesground white pepper or black pepper
2eggsbeaten
2Tblschopped scallions
2tspchili oiloptional
pinchred pepper flakesoptional
Instructions
Whisk to combine the corn starch and water. Set aside.
Add broth and water to a large pot over medium heat. Bring to a boil. Add tofu and mushrooms, cook for 2 minutes.
Add soy sauce, vinegar, dark soy sauce, and pepper. Stir to combine. Add the corn starch mixture, stir continuously for several minutes to thicken the soup. Turn off the heat.
Swirl the beaten eggs into the soup. Count to 10, and then using a pair of chopsticks, stir 3 times in a clockwise direction. This will form silken egg threads in the soup.
Add the scallions, chili oil and red pepper flakes, if using (taste your soup to determine the heat level that's right for you). Serve immediately or reheat gently before serving.