Tom Yum can be made with a number of ingredients. The version given here is for a simple tom yum het (mushroom soup), but it can also be tom yum kai (chicken), tom yum moo (pork), tom yum neua (beef), or tom yum khoong (shrimp), by simply substituting the mushrooms for another flavor ingredient. You can also mix and match to suit yourself... Note: the Thais serve the soup with the rest of the meal, usually in a large soup tureen, and each diner serves themselves, and uses it to wash out the mouth between selections from the other foods on offer. ingredients: 2 pounds fresh mushrooms (or other ingredient) cut into convenient spoonable size pieces... 2 stalks of lemon grass, bruised (this isn't eaten, but is an essential flavorant) 2 "kaffir" lime leaves (use lime zest if you can't get it) 2 coriander [cilantro] plants, chopped. 10-15 prik ki nu (birdseye chilis) thinly sliced. 2-5 dried red chilis. the juice of 3 or 4 limes 2 or 3 tablespoons of sliced bamboo shoots or coconut shoots 2-3 tablespoons of fish sauce. 1-2 tablespoons "chilis in oil" the "chilis in oil" or nam prik pao can be bought in small glass bottles from oriental specialty stores. You can also make your own: nam prik pao 4 tablespoon oil 3 tablespoon chopped garlic 3 tablespoon chopped shallots 3 tablespoon coarsely chopped dried red chillies 1 tablespoon fermented shrimp paste 1 tablespoon fish sauce 2 teaspoons of sugar heat the oil: add the garlic and shallots and fry briefly, remove from the oil and set aside. Add the chilies and fry until they start to change colour, then remove them and set them aside. In a mortar and pestle pound the shrimp paste, add the chillies, garlic and shallots, blending each in before adding the next. Then over low heat return all the ingredients to the oil, and fold into a uniform paste. The resulting thinck, slightly oily red/black sauce will keep almost indefinately. If you wish you can add more fish sauce and/or sugar to get the flavour you want. -- The fresh chillies should be bruised in a mortar and pestle. The dried chilies should be heated first, then crumbled into the fresh chilies. Beat the lemon grass with the grinder of the mortar and pestle (it's called a 'sa' in Thai, I'm never sure whether it is the mortar or the pestle in english...) or the back of a cleaver. Heat about 3 cups of water to boiling point, add all the ingredients, and stir constantly until cooked (it doesn't take long for mushrooms, longer for chicken or shrimp, and longest for beef). variation : use three cups of thin coconut milk instead of water, the result is tom kha, rather than tom yum...Special thanks to - Muoi Khuntilanont.