Professionals use fondant to cover their cakes with a smooth, satiny finish. Bring this cake decorating technique home for your own projects. Covering basic round or square cakes is straightforward, and irregularly shapes, with practice, are no harder to cover. The trick to cutting a sheet of rolled fondant to the size needed is to use the baking pan as a template.
Spread 2 cups buttercream frosting over the entire cake, smoothing the frosting to a thin layer with a spatula. This crumb coat will hold the crumbs against the cake, make the fondant appear smoother and help to adhere the fondant to the cake.
Dust a work surface lightly with powdered sugar, and roll the fondant with a rolling pin to 1/8 inch thick and a longer, wider oval than the number pan.
Place the number-shaped pan on top of the fondant in the middle, and flatten out the fondant with the rolling pin until the pan comfortably fits in the center with 3 inches of space on all sides.
Lift the rolled fondant gently from the work surface and drape it over the frosted cake.
Press the edges of the fondant down against the top and sides of the cake with your hands.
Trim away excess fondant from irregular corners and dampen the edges of the cut with a wet paper towel. Piece the edges together and smooth the seam with your fingers.
Pat the entire surface of the fondant-covered cake lightly with a damp paper towel to remove any remaining powdered sugar from rolling.