Hollandaise

• 4 oz (100 g) butter
• 2 tablespoons white wine vinegar

Melt the butter in a saucepan over low heat and allow to cool slightly. Boil the vinegar in a separate saucepan until reduced to a scant tablespoon. Draw off the heat and add the cold water, then add the egg yolks. Whisk over low heat for several minutes until thick and frothy. Draw off the heat again and slowly whisk in the warm (not hot) butter, then whisk in the lemon juice and season with s