In the container of a blender, combine the egg yolks, mustard, lemon juice and hot pepper sauce. Cover, and blend for about 5 seconds.
Place the butter in a glass measuring cup. Heat butter in the microwave for about 1 minute, or until completely melted and hot. Set the blender on high speed, and pour the butter into the egg yolk mixture in a thin stream. It should thicken almost immediately. Keep the sauce warm until serving by placing the blender container in a pan of hot tap water.