Cream Sauces Thickened with a Liaison

These sauces could also be called custard sauces, since, containing egg yolks, as they cook, they thicken exactly as a stirred custard would around 160° to 165°F, and should never be overheated or boiled. Since, unlike a dessert custard, a savory custard sauce does not contain any sugar, it thickens even faster than a dessert sauce. See the English custard techniques for a refresher.

As you can read, a liaison is a mixture of egg yolks and cream added to a classic flour-bound velouté to enrich it. The same liaison, only richer in egg yolks was used in classic cuisine, and is still used very occasionally, to thicken the gravy of such delicious dishes as braised sweetbreads, or braised fish and shellfish such as turbot, Chilean sea bass, and lobster.