I was naive enough to let my kid browse through this site when he was about to turn three. We looked at all the beautiful Nemo-cakes, and he pointed at the largest one and cried: "That one! please, mommy!" How could I resist?
I read a lot of descriptions on this site, and they really helped. Thank you all!
Since I'm useless at modeling, I bought a set of miniature Nemo-figures on Ebay. The smallest ones (Marvin, Dory, Gil etc.) were just perfect in size.
I started out making starfish, seahorses and shells from sugarpaste. I used a mold for this, and painted them with food colors.
I used plain white sponge-cake, and put each of the cakes on a cardboard plate, which I cut in the same size as the cake. Each cake was divided in three layers. Between layer 1 and 2, I put a thick spread of chocolate ganache made of mars bars.
Between layers 2 and 3, I put strawberry mousse. I covered the cake with Swiss Meringue Butter Cream (SMBC) and put it in the fridge for a while.
I had about two pounds of sugarpaste, and I dyed half of it blue using Wilton's Royal Blue. I then rolled the colors out together to get a marbled effect (which made the "ocean" look a little more alive). Unfortunately, every time I re-rolled the paste, the marbling was less visible, so the bottom cake is almost entirely blue.
I assembled the layers using straws with wooden dowels inserted to stabilize the cake. It worked well, but I had to bring tweezers to the party to remove the material when the cake was cut.
I piped decorations using colored and plain SMBC, and glued the decorations in place with royal icing. I put Nemo and two other characters on top with the candle.
The cake turned out great, and my son was really happy.