A classic French emulsified sauce for grilled meat, especially steak, made by whisking egg yolks with melted butter over gentle heat and flavoring with a reduction of vinegar, shallots, and tarragon. It is essentially hollandaise with the lemon replaced by a tarragon-vinegar reduction, giving it a distinctive anise-herb character. The technique demands patience: the yolks must thicken to a ribbon without scrambling, and the butter must be incorporated gradually to form a stable, glossy emulsion. Served warm, never hot, it is one of the great steakhouse sauces, its richness cutting through charred beef beautifully. Like all egg-emulsion sauces it is perishable and must be made fresh and held carefully, a delicious reminder that classical technique rewards attention.