Remove the husks from the tomatillos. Put the tomatillos, onion, garlic, and jalapeños in a large saucepan. Add water just to cover and a good spoonful of salt. Bring the mixture to a boil.
Pour the mixture into a shallow dish. When it’s quite cool to the touch, add the chopped cilantro and puree in a blender to obtain a bright green, frothy salsa.
Pour the salsa into a serving bowl.