Heat a dry griddle or heavy skillet over moderate heat until hot but not smoking. Toast chilies, 1 or 2 at a time, pressing down with tongs, a few seconds on each side to make more pliable.
Wearing rubber gloves, remove stems, seeds, and veins.
In a blender, purée the toasted chilies with remaining ingredients until the mixture is completely smooth.
Sauce may be made 2 days ahead and chilled, covered.
