Melt butter in a saucepan until bubbling hot.
Place egg yolks, lemon juice, salt, and pepper in a blender jar or food processor bowl.
Cover and mix until just combined.
Remove top and with machine running, pour hot butter into machine in a slow, steady stream.
Serve sauce immediately or keep warm in a double boiler thermos bottle.
Don't let the sauce boil or it will curdle and separate.
Then wash and throughly dry the blender.
Place an additional egg yolk in the container and while the machine is running, pour the hollandise mixture into the container in a slow, steady stream.
Process until thickened.