Tomatillos look like small green tomatoes (of which they are a distant relative) covered with a papery husk. They have a bright, lemon-like flavor, which is excellent with spicy food or alongside grilled items. Look for tomatillos that are firm but not rock-hard with their husks more or less intact (split open is fine, but you don't want them to have been handled so much that the husks are ripped off). The papery husks on tomatillos are pretty, but they need to be removed before cooking. Rinse de-husked tomatillos – they may feel a bit sticky, that's okay.