Whisk the egg yolks and lemon juice together in a stainless steel bowl until the mixture is thickened and doubled in volume.

Place the bowl over a saucepan containing barely simmering water, ensuring the bottom of the bowl does not touch the water to create a double boiler.

Whisk the egg mixture rapidly and constantly, maintaining low heat to prevent the yolks from curdling.

Slowly drizzle in the melted butter in a steady stream while whisking vigorously until the sauce is thickened and emulsified.

Remove the bowl from the heat and whisk in the salt and cayenne pepper.

Serve immediately or maintain in a warm water bath at approximately 145 degrees Fahrenheit for no more than 30 minutes.