Poblano pepper or poblano chiles are a dark (sometimes almost black) green chile with a rich flavor that varies from mild to snappy. The darkest poblanos have the richest flavor. This chile is about 2 1/2 to 3 inches wide and 4 to 5 inches long, tapering from top to bottom in a triangular shape. The every best pobanos are found n central Mexico, though they are now also grown in the U.S. Southwest.
Fresh poblanos can be found in Latin markets and in many supermarkets. Their peak season is summer and early fall. They’re also available canned. Ripe poblanos turn a reddish-brown color and are sweeter than the green. In their dried state they’re known as ancho or mulato chiles.
Poblanos can be used in a variety of dishes, but are perhaps best known as the chile of chioice for chiles rellenos.
Source: Food Lover’s Companion; Sharon Tyler Herbst and Ron Herbst; 2009