1Combine chiles and tomatoes in a small saucepan, cover with water, and bring to a boil over medium-high heat. Cook until chiles and tomatoes have softened, about 5 minutes.
2With tongs or a slotted spoon, remove chiles and tomatoes from water and place in a blender along with remaining ingredients. Pour in 1 1/4 cups of the chile cooking liquid. (You may have to do this in batches to avoid overflowing.) Cover and blend on high until smooth, about 4 minutes.
3Season well with salt and serve immediately, or cover and refrigerate for up to a week.