Pour the fat from the kettle, add the onions, and saute them, stirring, for 1
minute. Add the
vinegar and the
wine and boil the liquid, scraping up the
brown bits, until it is reduced by half. Add the
broth, the tomatoes, the dried
tarragon, if using, and the
chicken, bring the mixture to a boil, and simmer it, covered, for 20 to 25 minutes, or until the
chicken is cooked through. The
chicken may be prepared up to this point 1 day in advance