In small saucepan, stir egg yolks and lemon juice briskly with wooden spoon.
Add half the butter; stir over very low heat until butter is melted.
Add remaining butter, stirring briskly until butter is melted and sauce thickens.
Serve hot or at room temperature.
Note: Leftover sauce can be stored covered in refrigerator for several days.
Before serving, stir in small amount of hot water.