Step 1

In a saucepan, bring the vinegar and wine to a boil with the shallots and tarragon sprig. Season with pepper. Reduce until only about 45 ml (3 tablespoons) of liquid remains. Strain.

Step 2

In a bowl over a saucepan of simmering water, with a whisk, beat the vinegar reduction and egg yolks until thick and foamy.

Step 3

Remove from the double boiler. Off the heat, drizzle in the butter, whisking constantly. Add the chopped tarragon. Adjust the seasoning. If the sauce seems too thick, whisk in a little hot water. Keep at room temperature and just before serving, place back on the double boiler, whisking for just a few seconds, to warm it up.