Bearnaise sauce

1. Melt the butter, skim off any frothy bits and pour off the golden oil, discarding the milky solids. Set aside until lukewarm. 2.Put the wine and vinegar in a small pan with the bay leaf. 3. Strain the vinegar into a bowl with the egg yolks and water over a pan of barely simmering water. Beat with an electric whisk for 5-10 mins until thickened and ribbons form. 4. Remove from heat and slowly add the melted butter, whisking all the time, until it has all be incorporated. Season with salt and pepper and add chopped tarragon leaves. 5. Keep warm by placing the bowl back over the pan of water, off the heat and stir occasionally to stop a skin from forming.