Put the chiles in a bowl and pour boiling water over them. Let soak for 1 hour. Drain. Remove and discard the stems and seeds.
In a dry, hot skillet, toast the coriander and cumin seeds until aromatic and beginning to change color. Transfer to a mortar and grind with the pestle. Be sure to cup your hand over the mortar so the seeds don’t fly out.
In small batches, add the lemong