Remove the stems and seeds from the chiles. Perfume the chiles and cumin by heating them in a heavy skillet over a medium flame. DO NOT ALLOW CHILES TO CHAR! Burned chiles can become exceedingly bitter tasting.
Transfer the chiles and cumin seed to a coffee grinder. It may be necessary to tear the chiles into pieces, so as to fit them into the grinder's compartment. Process the mixture into a very fine powder.