Vegetable Egg-Drop Soup

"The ingredients here are healthy and simple, and each of them contributes to the taste characteristics and color contrast," says Chef Martin Yang. North Chinese soup is also versatile; don't add chicken to make it vegetarian, or add fresh water chestnuts for more texture.
Soak the mushrooms in a bowl with 1 1/2 cups of warm water until they are tender, 20-25 minutes. Remove the mushrooms, preserving the liquid. Cut off the stems with scissors and discard. Slice the mushrooms on a 1-inch-wide diagonal, then slice into lozenges.Meanwhile, lay the chicken flat on a work surface and hit it with the point of a Chinese chef's knife to flatten it to 1/4 inch. Slice into about 1/2-inch-wide longitudinal strips, then slice into lozenges. "I use 1 serving of meat for 3-4 servings of vegetables," notes Yang.In a bowl, combine the chicken with 1 tablespoon of cornstarch. soy sauce and 1/2 tsp white pepper. Set aside.Bring the broth, mushroom steeping liquid, and ginger to a boil in a large covered saucepan over high heat. Reduce the heat to medium-high and add the carrots and mushrooms. "Don't add everything together, otherwise it will be overcooked. In Chinese cuisine, everything should be crispy."Cook under the lid for 5 minutes, then add the onion, celery and zucchini. Cover, bring to a gentle simmer and cook until the onion is soft and crisp, 2-3 minutes.Add the chicken, tomatoes, coriander stalks, remaining 1/4 tsp white pepper and 2 tsp soy sauce, salt and oil to taste. Cook under the lid until the chicken is tender, another 3 minutes.Using chopsticks or a fork, beat the eggs in a bowl until the whites are completely smooth, but not so smooth that foam forms. "If they foam up, they'll float up from the top and be dirty," Yang warns.Turn off the heat under the soup. While stirring very slowly with a ladle, gradually pour in the eggs. Garnish with coriander sprigs.* To peel a tomato, cut it into slices and run a sharp knife between the skin and the pulp.