Roast the dried chili peppers, tomatoes, and a little onion and tomato in a dry frying pan for a few seconds.
Step 2: Soak the Chilies
Place everything in a pot of boiling water for 6 to 8 minutes. Leave to soak until the peppers swell with water. Do not completely submerge them in water.
Step 3: Blend Everything
Add the chili peppers, garlic, onion, tomatoes, vinegar, salt, and some of the water used to soak the chili peppers to a blender. Blend the ingredients until smooth.
Step 4: Simmer the Sauce
Pour the mixture into a pan and leave it on low heat for 10 minutes. It will darken in color and the flavors will blend perfectly.
Step 5: Cool & Store
Let it cool, then transfer to a glass jar. Place it in the refrigerator. Believe it or not, the flavor of this spicy Mexican sauce gets even better after a day or two.