 This assumption is supported by the fact that the restaurant was in the former residence of Henry IV of France, a gourmet himself, who was from Béarn, a former province now in the department of Pyrénées-Atlantiques, in southwestern France.Like Hollandaise sauce, there are several methods for the preparation of Béarnaise sauce.The most common preparation is a "bain-marie" method where a reduction of vinegar is used to acidulate the yolks.