Begin by melting the unsalted butter in a small saucepan over low heat until fully melted but not browned.
Add the egg yolks, salt, pepper, and lemon juice to the blender. Blend on medium speed until thick and pale, about 30 seconds.
With the blender running, slowly pour the melted butter into the egg mixture in a thin stream to emulsify the sauce.
Check the consistency and adjust with warm water if too thick. Taste and add more salt or lemon juice if desired.
Serve immediately over dishes like eggs benedict or steamed vegetables.
