Toast the chiles on a comal or griddle, in a dry cast iron skillet, or on the grill. Be careful not to burn them--you want to soften and bump up the flavor.

Cut off and discard the tops, keeping most of the seeds. (New Mexico chiles are mild; the seeds hardly add any picante heat. See note.)

Place the chiles in a bowl and cover with the boiling water. Weigh them down with a small plate to keep them submerged. Set aside for 10 to 15 minutes.

Drain the chiles, reserving the soaking water.

Place the chiles in the blender. Pour in the olive oil, 1/2 cup of the soaking liquid, salt, vinegar, and garlic, if using. Blend until you have a smooth puree. Dip a spoon to check thickness—depending on how I plan to use the dressing, I might add another tablespoon of the soaking water. Taste; add more salt if needed.

Strain through a wire sieve, pushing through as much of the smooth puree you can. You will have about 2 tablespoons of skin/seeds left in the strainer.