In classical cookery, a mixture used to thicken and enrich soups and sauces, most famously a liaison of egg yolks and cream stirred into a velouté. Flour-based liaisons, including roux and beurre manié, thicken through starch gelatinisation, while egg yolk liaisons add body and a silky sheen. The technique demands care: the liaison must be tempered with hot liquid and never boiled afterwards, or egg-based versions will curdle. Though the term comes from French cuisine, the principle appears worldwide wherever soups and sauces are finished. Modern kitchens sometimes replace traditional liaisons with starches or vegetable purées for lighter or allergen-free results.