In a saucepan simmer the fresh tomatillos in salted boiling water to cover for 8 to 10 minutes, or until they are tender, transfer them with a slotted spoon to a bowl, and let them cool. (Alternatively, use a drained 11-ounce can tomatillos, see note above.) In a food processor or blender, puree the tomatillos with the coriander, to taste, the garlic, and salt, to taste, and transfer the mixture to a bowl. Halve and pit the avocados, chop the flesh, and stir it into the tomatillo mixture. Serve the salsa with tortilla chips or with hamburgers, grilled meat, or fish.