As noted previously, sauces that have been greatly reduced or cooked for long periods will often end up tasting flat. A small bouquet garni containing a sprig of thyme, a piece of bay leaf, and a small bunch of parsley can be simmered with the reduced stock for about an hour before the stock is strained and added to the sauce’s flavor base. The aromatic flavor of the herbs will help restore the stock’s flavor.
A quick way of refreshing the flavor of almost any sauce is to finish it with freshly chopped parsley, chervil, or chives. None of these herbs will overpower the sauce, either when used alone or in a fines herbes mixture without tarragon.