Chinese Hot Sour Soup

This fragrant soup only takes a short while to prepare. (This is not an authentic recipe - in China, coagulated chicken or pig blood is used to thicken the soup. I use cornstarch instead!) The secret to hot sour soup is the ground white pepper. Use a good quality finely-ground white pepper. Start with 1/4 teaspoon and add more if you want a spicier soup. Feel free to substitute (or add) shredded chicken if you desire.
  
 1 quart chicken or vegetable stock
 8 oz. fresh shiitake mushrooms, stems removed, sliced thin
 2 Tablespoons soy sauce
 3 Tablespoons rice vinegar
 1 Tablespoon dry sherry (optional)
 1 teaspoon sesame oil
 1 teaspoon salt
 1/4 to 1/2 teaspoon ground white pepper
 8 ounces firm tofu, cut into thin strips, about 1 inch long
 4 green onions, sliced (separate white and green sections)
 1/4 cup water
 2 Tablespoons cornstarch
 1 egg, beaten
 
In a medium soup pot, heat the broth and the sliced mushrooms. Bring to a boil. Reduce heat and simmer for about 15 minutes, stirring occasionally. Stir in the soy sauce, vinegar, sherry, sesame oil, salt, and white pepper. Carefully, add the tofu and white ends of the onions. Return to a simmer.
 
Mix the water and cornstarch in a small bowl, add to the soup while stirring and continue to stir until it thickens - just a minute or so. While stirring in a circular motion, slowly pour in the beaten egg - then stop stirring! Let the mixture sit, undisturbed for about 30 seconds! (This will allow the egg to cook in pretty strands.)
 
Serve the soup in bowls and garnish with the green ends of the onion.
 
This recipe makes enough soup for 4-6 people as a first course.