Peppers can be roasted over an open flame or under the broiler in an oven.
To roast over an open flame on the stove:
Hold the pepper with tongs over a medium flame, turning occasionally until evenly charred.
In an oven under the broiler:
Arrange chiles in a single layer in a baking pan or sheet and place under hot broiler and allow them to char evenly, turning occasionally.
The skin should be blackened and blistered, place peppers in a paper or plastic bag, or a pan with a tight fitting cover. Seal or cover and allow to cool.
They will deflate, shrivel and look rather sad, but their skin will easily lift off, revealing a silky flesh underneath. Remove seeds and stems (if not using for chile rellenos) and use as directed in recipe.