Place chiles in a heatproof bowl and pour boiling water over the chiles to cover. Let soak at least 30 minutes or up to an hour.
Meanwhile, heat broiler to high. Place tomatoes and garlic cloves on a baking sheet and broil until lightly charred, about 5 minutes. Turn the garlic occasionally so it browns on all sides. Set aside until cool enough to handle.
Remove garlic from the skins and place in a blender. Add tomatoes, and salt then lift the chiles from the water (reserving water) and place in the blender.
Blend on high until smooth, adding some of the chile water if it is too thick. Taste and add more salt as needed.