A liaison is a mixture of egg yolks and heavy cream that is used to enrich a soup or sauce at the end of the cooking process (usually 1 part yolk to 3 parts heavy cream. Aside from enriching and giving the final dish a silky texture, a liaison also has some thickening power.

For food safety reasons, sauces and soups that are stored in the refrigerator always need to be brought up to the boil during reheating. Because of this, a liaison should not be added to sauces or soups that will be stored in the refrigerator because the high heat during reheating could cause the eggs in the liaison to curdle. This is why it is best to add the liaison after the sauce or soup has been reheated to the proper temperature.