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.
Heat olive oil in the stock pot.
Add a strainer over the stock pot.
Carefully strain the sauce into the pot, using the back of a spoon.
Be very careful. It can splatter.
Bring to a simmer.
Cook the sauce for 8-10 minutes.
Taste for salt.