1. In a meduim saucepan of boiling water, cook tomatillos over high heat until barely tender, 3 to 5 minutes. Drain and place in a food processor or blender. Process to a coarse puree.
2. In a medium bowl, combine tomatillos with onion, garlic, serrano peppers, cilantro, sugar and salt. Stir to mix well. Serve right away or set aside at room temp for up to 3 hours.
