Beurre blanc

Beurre blanc, French for "white butter", is a warm sauce made by whisking cold butter into a small amount of reduced white wine, vinegar and shallot. It has no egg and no flour. The result is pale, glossy and tangy, and it is a classic partner for fish, shellfish, asparagus and leeks.

How to do it

1. In a small pan, simmer 60 ml (1/4 cup) dry white wine, 60 ml (1/4 cup) white wine vinegar and 1 finely chopped shallot until only about 2 tablespoons of liquid remain.
2. Lower the heat to very low. Add 1 tablespoon of cream if you want a sturdier sauce.
3. Whisk in 200 g (about 14 tablespoons) of cold butter, cut in cubes, a few pieces at a time. Add the next pieces only once the last ones have melted into the sauce.
4. Season with salt and white pepper. Strain out the shallot if you want it smooth.

How to tell it is done

The sauce is thick enough to coat a spoon lightly, looks opaque and creamy, and has no pools of clear fat.

Why it works

Butter is already an emulsion of fat, water and milk solids. When cold butter melts slowly into a warm, acidic liquid, the milk proteins keep the fat spread in tiny droplets, so the sauce stays creamy. This is the same method as monter au beurre, just with much more butter.

Common mistakes

• Letting the sauce get too hot. Above about 60°C (140°F) it starts to split into oil and liquid.
• Letting it get too cold, so the butter firms up. Keep it warm in a thermos or a bowl over warm water.
• Adding the butter all at once.
• Reducing too little, which gives a thin, sharp sauce.

If it breaks, whisk a tablespoon of cold cream or water in a clean pan and slowly whisk the broken sauce back into it.

Where it comes from

Beurre blanc comes from the Loire Valley around Nantes, where it was served with river fish such as pike.