Ingredients:

  Amount  Measure       Ingredient -- Preparation Method
--------  ------------  --------------------------------
   3      cups          water
   2 1/2  teaspoons     salt
   2      cloves        garlic
   4                    fresh serrano chili peppers
   1      pound         tomatillos -- husks removed
     1/2  cup           fresh cilantro -- (fresh
                        coriander) sprigs
     1/4  cup           onion -- finely chopped

Preparation:

In a saucepan over high heat, combine the water and 1 teaspoon of the salt and bring to a boil. Add the garlic, chilies and tomatillos and cook, uncovered, until soft, 8-10 minutes. Drain, reserving 1/2 cup of the liquid. When cool enough to handle, stem the chilies and tomatillos. In a blender or in a food processor fitted with the metal blade, combine the garlic, chiles, tomatillos, reserved liquid, cilantro and remaining 1-1/2 teaspoons salt. Process to form a smooth puree, then transfer to a bowl. Stir in the chopped onion. Let the salsa cool to room temperature, then serve. The salsa can be stored tightly covered in the refrigerator for up to 1 week. Found on most tables in Mexican homes and restaurants, this versatile condiment enhances any savory dish. It is made with tomatillos, which are known in Mexico as tomates verdes; and although they aren't, in fact, related to tomatoes, their size, shape and texture are similar. You'll find them fresh, covered in their brown papery husks, in ethnic markets, well-stocked food stores, or in fruit and vegetable shops; they are also sold canned. Source: Mexican Favorites, Williams-Sonoma Kitchen Libra