Ingredients:

  Amount  Measure       Ingredient -- Preparation Method
--------  ------------  --------------------------------
   1      cup           white onion -- chopped
     1/2  tablespoon    garlic -- minced
   1      tablespoon    unsalted butter
     1/4  cup           sherry vinegar
   3      whole         guajillo chiles -- stems removed and
                        -- crushed
                        (1/2 cup)
   1      cup           black coffee -- strong
   1 1/4  cups          tomato puree
     1/3  cup           molasses
     1/2  teaspoon      salt
     1/2  teaspoon      freshly ground black pepper

Preparation:

Sauté onion and garlic in butter over low heat for 10 minutes -- being careful not to burn the garlic. Deglaze the pan with sherry vinegar. Add all other ingredients and simmer over low heat until the chiles are very soft. Puree the sauce in a blender until very smooth. Strain through a sieve.