Hollandaise sauce is an emulsion of butter and lemon juice using egg yolks as the emulsifying agent, usually seasoned with salt and a little black pepper or cayenne pepper. It is a French sauce, so named because it was believed to have mimicked a Dutch sauce. Hollandaise sauce is well known as a key ingredient in eggs Benedict. The sauce is one of the five sauces in the French haute cuisine mother sauce repertoire.Hollandaise requires some skill and knowledge to prepare; care must also be taken to store it properly after preparation. Properly made, the sauce should be smooth and creamy. The flavor should be rich and buttery, with a mild tang added by the lemon juice and seasonings. It must be made and served warm, not hot. If the ingredients are emulsified improperly by over- or under-heating them they will separate, resulting in the sauce "breaking" from the emulsion and the yolks coagulating from excessive heat. The sauce may be portioned and frozen for future use. When ready to use, let it come to room temperature; some stirring may be required.