The primary ingredient in hollandaise sauce is egg yolks. This classic sauce, often used in dishes like Eggs Benedict, is made by emulsifying the egg yolks with melted butter and a bit of lemon juice or vinegar. The meticulous process involves carefully whisking the egg yolks while adding the warm butter to achieve a creamy and smooth texture. Hollandaise is one of the five "mother sauces" in classic French cuisine, highlighting the role of eggs as a thickening agent. Its rich, buttery flavor pairs well with vegetables, seafood, and meats, making it a versatile addition to various dishes.