I used two 9×13 cake pans and stacked them. Then I trimmed the edges with a bread knife to get them square. The icing on the Spongebob Birthday Cake is buttercream and the bottom part is fondant. I just used the Wilton box kind because I didn’t need that much (it doesn’t taste that great though). I cut most of the fondant with a pizza cutter and laid it on the cake.

The eyes and mouth are fondant too. I put a thin layer of buttercream under it so it would stick to the cake. Then I just piped some legs and decorated the back board using a baggie and snipped the corner off.