Sauté onion and garlic until soft.
Add remaining ingredients, bring to a boil, reduce heat and simmer for at least one hour.
Purée sauce in a blender until smooth. Use the sauce right away or store, refrigerated for up to a week. Extra sauce can be frozen and used later.
Make Your Own Chile Pastes This recipe is for guajillo paste but the exact same method can be used for any whole dried chile.