Pasilla

The pasilla chile or chile negro is the dried form of the chilaca chili pepper, a long and narrow member of the species Capsicum annuum. Named for its dark, wrinkled skin, it is a mild to hot, rich-flavored chile. As dried, it is generally long and in diameter.
The fresh narrow chilaca can measure up to long and often has a twisted shape, which is rarely apparent after drying. It turns from dark green to dark brown when fully mature.
In the United States, producers and grocers sometimes incorrectly use "pasilla" to describe the poblano, a different, wider variety of pepper, the dried form of which is called an ancho if dried while green and a mulato if dried at maturity.

Use

Pasilla are used especially in sauces. They are often combined with fruits and are excellent served with duck, seafood, lamb, mushrooms, garlic, fennel, honey, or oregano. They are sold whole or powdered in Mexico, the United States, and the United Kingdom.
Pasilla de Oaxaca is a variety of smoked pasilla chili from Oaxaca used in mole negro.