Brush onion, tomatillos,corn and chile with olive oil. Grill vegetables on medium heat with lid closed as much as possible, until onions are slightly charred, tomatillos are soften and begin to collapse, corn is tender, and the chile is softened and slightly charred, turning as needed. (About 10 minutes for onions and 12 to 15 minutes for chiles and tomatillos.) Place chile in small bowl cover with plastic to steam for 10 minutes.
Peel skin from chile, discard. Remove stem and seeds. Place vegetables (except corn), cilantro, brown sugar and 1/4 tsp salt in blender or food processor. Whorl until puréed, stir in corn. Add more brown sugar and salt to taste.
Go to full version of