Source :Knorr Classic Sauces, Hollandaise Sauce Mix

Hollandaise means Holland-style or from Holland. This is a French sauce that originated in 19th century French cuisine. Most historians agree that it was originally called Sauce Isigny after a town in Normandy known for its butter. During World War I, butter production came to a halt in France and had to be imported fromHolland. The name was changed to Hollandaise to indicate the source of the butter and was never changed back.