You can flavour the basic egg yolk and butter sauce any way that you want. For instance just add chopped mint instead of tarragon when serving lamb.
Melt the butter and keep hot.
Boil the wine and vinegar with the shallot and pepper (and also the tarragon if using dried) until reduced by half.
In a bowl, whisk the egg yolks. Reduce speed of the whisk and pour the