Place the dried guajillo peppers in a bowl, add enough boiling water to cover them, and let soak for 30 minutes. You may need to use a small plate or saucer to keep them submerged.
Drain the peppers and remove the stems. If you want a very mild salsa, cut open and remove the seeds as well.
Place all ingredients into a blender. Puree until smooth, scraping down the sides of the blender as needed.
Refrigerate for at least one hour before serving to allow the flavors a chance to combine.