The term “fondant” can refer to a couple of different things. In many British cookbooks, for instance, a soft-centered chocolate cake is called “chocolate fondant.” The term primarily refers to a cooked mixture of sugar, water and cream of tartar that can be used either as a candy filling or as a frosting for a cake.
Fondant is made by boiling sugar and water to the soft ball stage. Cream of tartar is generally added just for stability. Once the mixture has been cooked and cooled slightly, it is very pliable and can be kneaded, rolled and molded into all kinds of shapes. For cakes, it is most often colored with some type of dye and rolled out into a sheet that can then be draped over a cake. Fondant will last for quite some time after it has been made, so it’s easy to make up a big batch and refrigerate it if you do a lot of cake decorating.
Even easier to use is ready-made fondant. This type of fondant is easy to find in craft stores and baking stores as an alternative to attempting to make it from scratch. To give it added stability and longevit, it is not made with the simple sugar-water-cream of tartar mixture alone, but uses preservatives (and often loads of extra sugar). Fondant can be flavored with anything, but the slightly chemical taste that often accompanies store-bought fondant is what turns people off to it as a decorating tool, when in fact the classic from-scratch fondant can actually taste quite nice.