Classic Beurre Blanc

• 125 g (4½ oz) butter, softened
• 3 tablespoons white wine vinegar

Chop the shallots very finely and throw them into a small saucepan with the vinegar and the water. Boil to cook the shallots and reduce the liquid. When the liquid has almost completely evaporated, put the pan over a bain-marie and incorporate the butter gradually, whisking over a very gentle heat.

When all the butter has been added, season the sauce with salt and pepper and strain it t