Fondant gives your cupcakes a silky-smooth surface, perfect for displaying icing flowers, figure piping and other decorations. The formula for covering cupcakes or mini cakes completely with rolled fondant is the same as for covering cakes. Measure opposite sides and the top of cake (baked without baking cups) across the center. Roll out fondant to that size, 1/8 in. thick. For example, a standard 2 in. wide cupcake, with two sides each 11/2 in. high, equals 5 in. diameter. It is easier to cover a cupcake bottom side up.