In a casserole, cook the Reims vinegar, the pepper, the shallots and the tarragon until you obtain the volume of a soup spoonful of liquid.
Strain and add a soup spoonful of cold water.
Incorporate the egg yolks and whisk vigorously.
Continue to whisk over a low heat for 4 minutes.
Away from the heat add the melted butter little by little, until the sauce thickens and becomes a continual trickle.
Add the chives and serve.