Step 1

Place egg yolks, lemon juice, and salt in a blender; blend until combined. Melt butter in a saucepan or in microwave. With blender running, slowly pour butter through opening in lid in a thin stream until sauce is thick, about 1 minute.

Step 2

Serve immediately or transfer to a bowl and cover with foil to keep warm; serve within thirty minutes. If sauce is too thick, thin to desired consistency by whisking in hot water one tablespoon at a time.