Hollandaise sauce mayonnaise and Béarnaise, the egg does not coagulate as in a custard; rather, the lecithin in the eggs serves as an emulsifier, allowing the mixture of the normally immiscible butter and lemon juice to form a stable emulsion. To make hollandaise sauce, beaten egg yolks are combined with butter, lemon juice, salt, and water, and heated gently while being mixed. Some cooks use a double boiler in order to control the temperature. Some recipes add melted butter to warmed yolks; others call for unmelted butter and the yolks to be heated together; still others combine warm butter and eggs in
French cuisine contrôlée" (AOC) (regulated appellation) laws. French cuisine was made important in the 20th century by Auguste Escoffier to become the modern haute cuisine; Escoffier, however, left out much of the local culinary character to be found in the regions of France and was considered difficult to execute by home cooks. Gastro-tourism and the "Guide Michelin" helped to acquaint people with the rich bourgeois and peasant cuisine of the French countryside starting in the 20th century. Gascon cuisine has also had great influence over the cuisine in the southwest of France. Many dishes that were once regional have proliferated in variations