Hot and Sour Soup

* From Martha Stewart's Recipe

Ingredients:
8 cups homemade chicken stock, or canned low-sodium chicken broth
2 teaspoons toasted sesame oil
2 cloves garlic, minced
1 small onion, cut lengthwise into 1/4-inch thick slices
4 ounces shiitake mushrooms, stemmed and sliced 1/4inch thick
2 carrots, peeled and cut into matchsticks
11/2 teaspoons grated fresh ginger
1 teaspoon freshly ground black pepper
pinch cayenne pepper
1/2teaspoon salt
3 tablespoons cornstarch
3 tablespoons low-sodium soy sauce
6 tablespoons rice-wine vinegar
1 large whole egg, plus 1 large egg white, beaten
3 large scallions, trimmed and cut crosswise into 1/4inch thick slices
6 ounces firm or extra-firm tofu, cut into 1/2inch cubes

Instructions:
1. In a 6-quart saucepan, heat sesame oil over medium-low heat. Add garlic and onion, and cover. Sauté, stirring occasionally, until translucent -- about 6 or 7 minutes. Add mushrooms and sauté until tender, about 5 minutes. Add chicken stock, carrots, ginger, black pepper, cayenne, and salt; bring liquid to a boil. Reduce the heat, and simmer until carrots are tender, about 3 minutes.
2. Place cornstarch in a small bowl, and slowly whisk in soy sauce until cornstarch has dissolved. Whisk in vinegar. Slowly whisk cornstarch mixture into soup. Simmer until soup is no longer foggy, 5 to 7 minutes. Turn off the heat.
3. Slowly pour beaten eggs through a perforated spoon into soup. Cover soup, and let stand 1 minute. Remove the cover, and gently stir. Add scallions and tofu. To serve, ladle into individual bowls.