Meringue buttercream is a frosting made by beating softened butter into a cooked egg-white meringue, giving it a light texture with a smooth, rich mouthfeel. There are three named versions, distinguished by how the meringue is made: Swiss meringue buttercream whips egg whites and sugar over a warm water bath before adding butter; Italian meringue buttercream beats whites with a hot sugar syrup; French buttercream instead uses whipped whole eggs or yolks rather than a true meringue. Swiss and Italian are the most common in professional baking because they hold up well at room temperature.
Meringue buttercream is used to fill and decorate cakes, cupcakes, and other pastries in French, Swiss, and other European baking traditions; it is a common covering for layer cakes but is not the binder used in croquembouche, which is held together with caramel.
Its flavor is primarily sweet with a light, airy quality from the meringue and a rich finish from the butter; vanilla, almond, and other extracts are common additions. It pairs well with fresh fruit and berries, which cut its sweetness, and with nutty or chocolate flavors.