Genoise: This type of sponge cake is made with whole eggs rather than just egg whites, which gives it a richer flavor than angel food cake. The eggs are combined with sugar and gently heated over simmering water, then whipped (heating the eggs allows them to be whipped to a greater volume). Genoise lacks much assertive flavor of its own, but it is often used to construct layered or rolled cakes when a lighter texture than a butter cake is desired. To add flavor and moisture, genoise cake layers are always moistened with a flavored syrup, and they are often sliced into thin horizontal layers and stacked with rich fillings such as buttercream. These layer cakes, common in the coffeehouses of Europe, are called "European-style" to distinguish them from American-style butter layer cakes, which generally have fewer, thicker layers.