Glazes are usually shiny, relatively dense, and very rich coatings for the outsides of cakes. They are applied in thinner layers than frosting. Frostings and other fillings, while often very rich, are lighter than glazes and are applied in thicker layers on the inside of cakes and sometimes on the outside as well. While melted chocolate can be used alone as a cake glaze, most chocolate glazes contain cream and/or butter to soften the glaze once it sets.
Ganache, the most popular glaze, is made by combining melted bittersweet chocolate and heavy cream and stirring the mixture until smooth. The hot ganache can be poured over cakes and left to set, or it can be used as a hot sauce for ice cream or profiteroles. You can change the texture and flavor of ganache by adding more or less chocolate to the cream or by whisking in butter, which will make the glaze stiffer when it sets. Ganache is easy to flavor with a small amount of strong coffee, liqueurs, or spirits such as whiskey, brandy, or grappa.