Can be prepared in 45 minutes or less.

Ingredients

　　10 ounces mushrooms, chopped fine

　　1 tablespoon unsalted butter

　　1 3/4 cups beef broth

　　3/4 cup water

　　1 1/2 tablespoons cornstarch

　　1 tablespoon soy sauce

　　1 tablespoon wine vinegar or fresh lemon juice, or to taste

　　2 scallions, sliced thin

　　In a saucepan sauté the mushrooms in the butter over high heat, stirring, until the liquid the mushrooms give off is evaporated and stir in the broth and the water. In a small bowl whisk together the cornstarch, the soy sauce, and the vinegar until the cornstarch is dissolved and stir the mixture into the soup. Bring the soup to a boil, stirring, and simmer it for 5 minutes. Stir in the scallions and salt and pepper to taste and simmer the soup for 1 minute more.