In your small sauce pan, bring a small amount of water to a boil. Once boiling, remove from the burner and place on another burner set to low.
Yolks and Juice
In your bowl, begin to mix the egg yolks and lemon juice. Whisk the mixture vigorously until the mixture thickens and increases twice in its volume.
Place Bowl on Pan
Once your egg mixture is thickened, place your bowl on top of the pan with the simmering water. The heat will aid in forming and thickening the sauce. Continue to whisk the mixture well.
Note: Be sure that the bowl is not making contact with the water as this may cause the eggs to begin to scramble.
While whisking, begin to add the melted butter to your eggs. Continue to stir the mixture until it thickens further and once again expands to twice the original volume.
Remove and Add
Once thickened, remove the bowl from heat and whisk in the salt and cayenne pepper making sure to mix it all well.
Set Aside and Use
Once mixed, set your bowl aside and cover. The sauce should be used as soon as possible. If it thickens too much, add a few drops of warm water and stir well once again.