Adapted from lickthebowlgood.blogspot.com
oz. (1½ sticks) unsalted butter, cut into cubes
tablespoon lemon juice
teaspoons white wine vinegar
Begin by clarifying the butter. Put the butter in a small saucepan and bring to a simmer. Remove from the heat, skim off any foam on the surface, and let cool for a few minutes. Carefully pour the butter into a jug, leaving and sediment behind. Half fill a saucepan with water and bring to a simmer. Put the egg yolks, lemon juice, vinegar and 1 tablespoon water into a medium heatproof bowl and whisk until fully combined. (You're making a double boiler here). Put the bowl over the water, making sure that it does not touch the water, and whisk about 1 minutes until the edges are thick and foamy. Slowly add the melted butter, whisking well until the sauce is thick and creamy. It should leave a trail if the whisk is lifted. Season well with salt and pepper.