A few tomatillos, and you've got a salsa with some serious zing.
Cover the tomatillos with water in a nonreactive saucepan and get it boiling. Let the pan simmer until the tomatillos soften and begin to burst, about 10 minutes.
Drain out the tomatillos. Place them in a food processor or blender, along with the onion, garlic, jalapeno peppers, cilantro, salt and pepper. Blend that stuff up until it's as chunky or smooth as you prefer.