Melt the butter gently in a small saucepan over low heat.

Whisk together the egg yolks and lemon juice in a mixing bowl until frothy.

Heat the mixture over a double boiler or a bowl set over simmering water, whisking constantly for about 5 minutes until it thickens slightly.

Pour the melted butter slowly into the egg mixture while whisking continuously.

Season with salt and a pinch of cayenne pepper to taste.