Roast whole dried chiles in an ungreased, very hot cast iron skillet, shaking the pan from time to time to avoid any scorching. This only takes a little under a minute. Remove the chiles from the pan, let them cool enough to be handled, and break them apart. Discard the stems, seeds, inner veins and any dark spots. Grind the pieces to a fine powder in a blender. Store the chili powder in a glass container in a cool, dark cupboard to retain its flavor.