4 egg yolks 2 Tbs tarragon vinegar 350gm butter (melted) Juice of one lemon Salt and pepper
Put egg yolks and vinegar in a large bowl over a pot of simmering (not boiling) water. Whisk rapidly and continually until you can form a figure eight in the mixture and it holds. Remove from heat and add butter very slowly while whisking continually. Whisk in lemon juice, salt and pepper. If the mixture is too thick then add warm water, one teaspoon at a time.
This sauce holds for a couple of hours and should never be refrigerated.