With a damp paper towel, wipe off any dust on the peppers.
Remove the stems, seeds, and veins of the guajillo peppers
Add 4 cups water and the cleaned peppers to a stock pot.
Put the lid on, and bring to a boil.
Turn heat off, leaving the peppers inside.
Wait for 5 minutes, or until the chiles are pliable.
Discard the water.
Rinse the pot and set aside until ready to use.
To a blender, add the rehydrated peppers, garlic, onion, cumin, and salt.
Add 2 cups water to the blender.
Blend until smooth.
Strain the sauce.
Return the sauce to the pot and bring to a boil.
Boil for 5 minutes.
Taste for salt.