Add the balsamic vinegar
, red wine vinegar, onion
, raisins, garlic, anchovies
, brown sugar, cumin seed, cloves, and celery seed to a large saucepan
and bring to a simmer
. Cook until reduced by two-thirds. Strain
the mixture, pressing on the solids to get maximum flavor. Discard the solids. The sauce will hold for 1 month in the refrigerator.