For Ethan's 3rd birthday we had a "Lightning McQueen" themed party complete with a Lightning McQueen cake. It was really fun to make...a bit of work but totally worth it. Starting last year I've been trying my hand and making his birthday cakes and have learned so much. They're certainly not perfect, and sometimes a bit of work, but totally worth it!
I don't know how professionals do it, but I thought I'd share a couple of tips, because I've found some things that really help make it easier.
1. I find a simple image online of what I want on top of the cake (make sure it is large enough to trace without super tiny details) I print this off and then trace it with a sharpe onto parchment paper.
2. I bake my cake a day or two in advance (I always use a boxed mix) and then freeze it until the day before I'm decorating (I decorate 1 day before the party). It's much easier to frost a frozen cake...this was a tip from my mom and it works...plus, your cake is super moist. I do not defrost my cake before getting started.
3. I frost my entire cake. When I'm done, I go back over my cake dipping my knife in a glass of very hot water and smooth the whole surface of the cake. I let this frosting set-up for about 30 min and then I lay the image on top of the cake and trace around it with a tooth pick or wooden skewer pressing firmly. Once you are done tracing you can lift off your parchment paper and see the indention of your image on the cake.
4. next it's just a matter of coloring in the lines :) you'll want some icing bags and some piping tips in various shapes and sizes. You can find these pretty inexpensive in the craft section at Wal-mart in the cake decorating isle (Michael's has a better selection).
5. I trace the outlines in black frosting using a small round tip. then fill in with colored frosting according to my picture. That's it.
Here was our final product:
I'm sharing this because it is totally doable! AND less expensive than getting it professionally done. There is a small start-up cost for your tips and bags, but I spent less than $5 on those. Then the cost of your cake mix. I used a friend's frosting recipe (super yummy) or I'm sure a canned frosting would be fine too.