Rich and elegant, the sauce known as beurre blanc — literally white butter — is one of the delights of the French table. It is made by incorporating butter bit by bit into a reduction of shallots and wine vinegar. The sauce ‘rises up’ like a mayonnaise — and can also break down if overheated or overcooled, so you need to be careful.
In principle, a beurre blanc should be made just before being brought to the table. But in practice it’s possible to make the sauce up to two hours in advance, providing you keep it in a warm place, for example over an unlit burner on the stovetop.
Beurre blanc is most often used in France as a sauce for fish. It is traditionally made with white wine vinegar, but I have found through practice that red wine vinegar (not balsamic) works equally well. This recipe makes enough to serve 4 generously.
1/4 pound (125 g.) unsalted butter
2 tbsp. wine vinegar
pinch of sea salt
Cut the butter into 8-10 pieces. Mince the shallot finely.
Bring the vinegar and the shallot to a simmer in a nonreactive pot — enamel is good.
When the liquid has nearly evaporated, remove from heat and begin adding the butter, bit by bit, stirring constantly with a wooden spoon to make an unctuous sauce. Wait until each bit has melted before adding the next. Add the salt.
When all the butter has been incorporated, pour the sauce through a sieve into a clean pot or bowl to remove the shallot.
To serve, drizzle a spoonful or two of warm sauce over each portion.