Some Asian markets now carry bags of pak chee farang leaves. If you can't get them, omit, or add a little more cilantro. In some markets they are labled with their Vietnamese name, ngo gal. Place water in 3 litre saucepan. Add lemon grass, line leaves and shallot and bring to boil. Add chiles and shrimp. Cook 2 minutes. Add straw mushrooms, lime juice, fish sauce and salt. Add tomato and cook just until heated, not soft. Turn unstrained soup into serving bowl. (Do not eat lemon grass and lime leaves.) Top with pak chee farang and cilantro leaves. Each serving contains about: 91 calories; 892 milligrams sodium; 86 milligrams cholesterol; 1 gram fat; 8 grams carbohydrates; 13 grams protein; 0.77 grams fiber.