Measure out all of the ingredients before you start so you can focus on cooking the pepper and garlic nicely.
Toast the ancho chili pepper in the oil on very low heat. Once it swells like a balloon, remove it from the pan and let it cool. (Don't discard the oil!)
Add the peeled garlic cloves to the same oil used to toast the peppers and continue cooking over low heat for about 2 minutes. Pay attention, because if you burn the garlic you should start over.Once the garlic has softened slightly, turn off the heat.
Remove the seeds from the toasted ancho chili by cutting off the top of the pepper with scissors and emptying it out.
Add the rest of the ingredients and continue to cook over low heat. Bring to a boil and simmer for 5 minutes. Stir the bottom of the pan with a spoon to prevent it from burning.
Pour the sauce into the blender, lock the lid securely and put a towel on top to prevent it from splashing up. Start on low speed and gradually increase to high speed. Blend until smooth.
Let the sauce cool before storing in a sealed container in the fridge for up to 5 days.