4 tbsp white wine vinegar
1 shallot, finely chopped
4 black peppercorns
a few fresh tarragon sprigs, chopped
2 medium (US large) egg yolks
75g/3oz/6 tbsp butter, at room temperature, diced
1 tbsp chopped fresh tarragon
salt and ground white pepper
1 Put the vinegar, shallot, peppercorns and tarragon sprigs in a pan. Bring to the boil and reduce to 1 tbsp. Cool, then strain.
2 Beat the egg yolks and reduced vinegarin a heatproof bowl. Put the bowl over a pan of barely simmering water and whisk for 3–4 minutes until pale and starting to thicken.
3 Beat in the butter, a piece at a time, until the mixture thickens and emulsifies. Do not allow it to overheat or the eggs will scramble and split. Remove from the heat.
4 Season to taste. Stir in the tarragon.