Pour about an inch of water into a large saucepan, bring to a simmer over medium heat, and reduce the heat to low.
Place egg yolks and 1 teaspoon of water in a medium mixing bowl and whisk until mixture lightens in color (1-2 minutes). Add the sugar and whisk for another 30 seconds.
Place the mixture over the simmering water and whisk for 3 to 5 minutes, until the mixture is thick enough to coat the back of a spoon.
Remove the bowl from over the saucepan and gradually add the butter one small piece at a time, and whisk until the butter is incorporated. Place the bowl back over the simmering water occasionally to the melt the added butter.
Add the salt, lemon juice, and cayenne pepper and serve immediately.