Add egg yolks and lemon juice to blender and process at medium speed until well combined.
With the motor running slowly add hot butter in a thin, steady stream. Continue blending until the mixture has thickened and becomes pale yellow.
If the sauce is too thick you can add up to 1 1/2 tsp of hot water if you wish. With the motor running slowly add water to thin until you have the desired consistency. The sauce should coat the back of a spoon.
Notes
See the "How To Make This" & "Tips For Success" sections above the recipe for more detailed information on the process.