Melt the butter over low heat in a small saucepan.
Remove any solid parts with a spoon. Peel and chop the shallots.
Place a small pan over medium heat and add the shallot, vinegar and whole peppercorns.
Reduce by half, then remove from the heat and add a little water to cool.
In a separate bowl, whisk together the egg yolks.
Then add them to the pan with the vinegar.
Return to the heat and stir, letting everything thicken for a couple of minutes.
Remove the pan from the heat and add the melted butter.
Stir briskly until you have a uniform sauce.
Finally, add the salt, pepper, chopped tarragon and chopped chervil. Stir delicately.