An ancho is a dried poblano chile. It has a mild to medium heat with a sweet fruity flavor with hints of cherry, prune, and fig. It's used often in Mexican cooking, especially in mole (MOH-lay).
Substitute ground ancho chile powder or mulato chiles (which are a little less sweet and a little more smoky).
The best dried chiles are the ones that have been sun-dried and not commercially oven-dried, which can make them bitter. Look for whole, not broken pods, with a uniform color. They should be be tough but still a little flexible. Be aware the dried chiles are often mislabled. An ancho chile is wider and more squat then a pasilla or New Mexico chile and is slightly translucent as opposed to opaque.
Pull off or cut off the stems and scrape out the seeds. Dried chiles can be crumbled or ground and added right to a dish. Or toast them lightly in a little hot oil in a skillet to intensify their flavor. If pureeing dried chiles for sauce, rehydrate them first by soaking them (toasted or untoasted) in boiing water for a half hour or so.
Dried chiles will keep for months in a cool, dry place, though they may become more brittle over time.