Beurre Blanc

White butter is the famous, some would say the notorious, sauce from Nantes, a traditional Breton center at the mouth of the Loire on France’s Atlantic coast. Beurre nantaise, as it is also known, is the bugbear of busy chefs, because if kept too long, it melts down from an elegant creaminess into an oily mess. At home, it isn’t such a problem. The very reduced and highly acid shallot-vinegar base easily emulsifies the cold chunks of butter plopped into it over very low heat.