This Spongebob Cake was made for my daughter turning 4. She is absolutely in love with Sponge-Bob. I made my first kid's birthday cake in March of 2011. "First Cake Ever". I got all the design ideas from coolest-birthday-cakes.com. I started with how to make roll out icing for my shapes. I had a 1/2 a bag of marshmallows and a bag of powered sugar and that was all I needed to get started. I heated the marshmallows on half power in the microwave for 2 minutes total checking after each minute. They were a light fluffy sticky mess. Perfect, I began to add powered sugar and mix till the mix was similar to that of sticky dough.
Now comes the fun part, I coated my hands in shortening and began to knead the mix and adding more powered sugar till it was thick like bread dough. Once I had my ball of icing I broke off pieces and added color and kneaded it some more, using powered sugar like you would flour for dough. I put my colored pieces aside and then rolled out my still white pieces for the shirt, teeth and eyes. My half a bag of marshmallows was more than enough for sheet icing. When applying the sheet icing I laid the pieces on a wet paper towel and flipped just before applying. This will take the powder sugar coating off ready to use.
I used cream cheese frosting from a tub and added yellow food coloring, and same tub of frosting dyed grey "attempted black". Like I said I'm new at this. I used a pizza cutter to cut the icing. Keeping the icing coated in powered sugar will make it easier to work with. Don't roll it too thin, it will fall apart. If the icing is feeling thick and hard to work with put a little shortening on your finger tips and re-knead the icing. The cake itself is just Duncan Hines box mix, double layer. I used a brown glass 13.5x9.5 greased with shortening then coated in a light flour dust. Baked at 325 for 35 minutes and it was done the first time, no extra time needed. The frosting was applied with a small zip lock bag with a very tiny hole cut in the corner. This took about 10 hours to make over all... That's with starting a 8:30pm kids still up wanting to help and lack of experience. I finished with cleanup and all at 5:00am. Good luck and happy cake making.