Foie gras is excellent for finishing sauces. Because of its high fat content, it will thicken a sauce and remain smooth provided it is not allowed to boil. When using partially cooked foie gras (mi-cuit) or terrine of American foie gras, mash together about equal parts foie gras and butter, then force the mixture through a fine-mesh drum sieve. Avoid using raw foie gras, which contains too much water.

Because foie gras butter is inherently unstable, it is a sound idea to add 2% liquid lecithin to the foie gras–butter mixture. Propylene glycol alginate (0.5%) can also be blended into a sauce’s hot liquid base for further stability.