Melt the butter in a saucepan, keep it at room temperature.
Peel and finely chop the French shallot.
Over medium heat, soften the French shallot in the white wine and vinegar, then allow to reduce until almost dry. Off the heat, add the egg yolks, whisking in the top part of a double boiler until the mixture becomes pale and thick. (Important: the temperature mustn’t go over 80°