Cut off the stems. (Scissors work well.) Cut a slit in the chiles and tap them over a bowl so the majority of the seeds fall out. Discard the seeds.
Place the chiles in a bowl and cover with the boiling water. Place a small plate on top to keep them submerged. Set aside for 30 minutes, or longer. (see note)
Heat the oil in a medium skillet. Add the strained puree and cook 3 to 4 minutes, stirring occasionally. The sauce should be the thickness of heavy cream. If it seems too thick, stir in a little more of the soaking liquid.
I soaked the chiles overnight with dandy—no problema—results.