Melt the butter. Put egg yolk, wine, 1⁄2 teaspoon salt and honey in a metal bowl. Whip in a hot water bath (do not boil!) to a thick light cream. Lift out of the water bath. Stir melted butter bit by bit in a thin stream into the egg yolk cream.
Stir in the mustard. Season hollandaise sauce with salt and cayenne pepper.