- In a heavy bottom saucepan, heat butter until melted and slightly foamy, but do not brown the butter.
- In mixer, beat egg yolks with the lemon juice, salt and hot sauce or pepper flakes. While mixing, gradually add the melted butter, then the water.
- Return the mixture to the saucepan over low heat, whisking until slightly thickened. Best if served immediately, but can be kept up to an hour by covering and placing saucepan on top of another pan filled with hot water. Lightly sprinkle with parsley or chives, if desired just before serving.