12 tablespoons (1 1/2 sticks) unsalted butter, chilled and cut into small pieces
1/2 teaspoon kosher salt
2 teaspoons freshly squeezed lemon juice
1/8 teaspoon cayenne pepper
Pour 1-inch of water into a large saucepan; over medium heat, bring to a simmer. Once simmering, reduce the heat to low.
Place egg yolks and 1 teaspoon water in a medium mixing bowl and whisk until mixture lightens in color, approximately 1 to 2 minutes. Add the sugar and whisk for another 30 seconds.
Place the mixture over the simmering water and whisk constantly for 3 to 5 minutes, or until there is a clear line that is drawn in the mixture when you pull your whisk through, or the mixture coats the back of a spoon.
Remove the bowl from over the pan and gradually add the butter, 1 piece at a time, and whisk until all of the butter is incorporated. Place the bowl back over the simmering water occasionally so that it will be warm enough the melt the butter. Add the salt, lemon juice, and cayenne pepper. Serve immediately or hold in a thermos to keep warm.