Though they’re sometimes folded into cake or cookie batters or fillings, meringues— sweetened egg foams—generally stand by themselves as a discrete element in a dish: as a frothy topping, for example, or a creamy icing, or a hard edible container, or melt-in-the-mouth decoration. A meringue foam must therefore be stiff and stable enough to hold its shape. The cook obtains both stiffness and stability by the addition of sugar and/or of heat. Meringues are often baked very slowly in a low oven (200°F/93°C) to dry them out into a brittle, pristinely white morsel or container. (The door of electric ovens should be left slightly ajar to allow the meringue’s moisture to escape; gas ovens are already vented.) When quickly browned in a hot oven or under the broiler—atop a pie, for example—the surface gets crisp while the interior remains moist. Poached in milk for the dish called Floating Islands, they are firm yet moist throughout.