My son wanted to have a Nemo cake for his 2nd birthday. We searched all over the internet for a pan, but couldn't find one and I wasn't satisfied with the other ideas I saw. So I found a Nemo coloring page online and printed it and enlarged it to the size cake I wanted. I cut it out to use as a pattern.
I made 3 9x13 cakes (2 butter recipe cakes, 1 chocolate)and after they cooled enough, I chilled them in the refrigerator. Once cold, I put the pattern of Nemo on the cake and cut out the various shapes. I wrapped each piece in plastic wrap and froze them.
Once frozen, I "glued" them together with frosting on a covered cutting board. I also spread a thin layer of white icing over the entire cake. (I kept the cake in the freezer until I was ready to ice the rest.)
My husband used the picture of Nemo for a reference point and used a cake tester to sketch out the lines on Nemo. I colored cream cheese frosting using Wilton's orange coloring, but decided that the best way to make black that tasted good was to start with chocolate icing and color it with Wilton's black.
I used Wilton star tips for all of the icing on the top, following the lines that my husband had drawn. When I was finished with the top, I iced the sides using a large tip (looked like basket weave). However, I would suggest doing the sides first, as it was difficult once the top was done.
To finish it up, we could not bear to stick a candle in Nemo, so we piled up icing to the side of him and stuck the candle in that.