For my son's 3rd birthday party, he really, really wanted a Lightning McQueen birthday cake. I searched the web for ideas on how to make a 3D Lightning cake, but they all used a marzipan layer on top, but I wasn't really familiar on how to use that so I wanted to go a more traditional icing route. I think it turned out great and now that I've sorted out how to make it all work it will be easy to replicate.
I started out by making a cake mix in a greased and floured 9x13" pan. Bake according to box's instructions and let cool on cooling rack.
Then I wrapped the whole cake in cling wrap twice and then put the whole cake in the freezer for at least 45 minutes (you could do it overnight as well). Freezing the cake helps firm up the cake so that it is much less crumbly when you cut it.
Then using a serrated knife I cut up the 9x13" cake into the pieces I needed to make the car. I cut one large rectangle 7x10." That left a 9x3 piece (on the right above) and a 10x2" piece (on the top above).
From the 9x3" piece I cut it to be about 6 inches long (this will be used for the top of the car and angled a bit to make the windshield. From the 10x2" piece cut it to be about 6" long as well and then cut it in half at an angle to create two triangular strips. Use of the triangular strips lay behind the "windshield" piece and then stand the other piece up on end to make the spoiler. From the corner pieces that are left, cut those in half in triangular pieces and use the rounded outside ends to create the rounded wheel fenders for the front hood on each side.
To assemble put a layer of icing on top of the 7x10" rectangle and assemble the cut pieces on top. I would recommend securing the back spoiler with some toothpicks in the back.
A front view of the car cake
Next cut out the holes for the wheels. With regular sized cup cakes you'll want to cut holes about 2 1/2" tall and 2" deep. Then wrap up the cake in cling wrap and stick back in the freezer for about 40-45 more minutes. (NOTE: I had already started icing the car cake before I cut out the wheels as I was making this all up on the go, so it would have been better to cut the holes first and then stick it back in the freezer to firm the cake back up again to put on my crumb layer of icing.)
While the car is in the freezer, you can coloring your icing. I used about 1 1/2 containers of vanilla icing in which I used A LOT of red food coloring. NOTE: the food coloring will change the consistency of your frosting to a little more liquidy. I think homemade cake icing would be more ideal as you could keep adding more powdered sugar to it to firm it up. I think you could do the same with the store bought frosting as well to firm it up a little.
When you take the car back out of the freezer, you will used about half of your colored icing to apply a crumb layer. Take a few strips of waxed paper and place them slightly under all the edges of your cake to keep your cake plate protected (you will remove these later). Then take an icing knife and spread a thin layer of icing to "seal up" the cake. Place the cake back in the freezer for another 40-45 minutes to harden up the crumb layer of icing.
When the crumb layer is chilled, take the cake out of the freezer and apply the final frosting layer. Use the icing knife to create a flat surface at the windshield and smoothed flowing lines to shape the car.
You will also want to freeze 4 regular sized cupcakes (I just made up a second batch of cake mix to make these and have extra cupcakes for the birthday party). When they are firm from the freezer, you can take a metal melon baller and cut out holes on the top. Also remove the paper wrappers from each cupcake.
Frost the cupcake tops with chocolate frosting and sprinkle them with black colored sugar. After removing the waxed paper from under the final iced cake, carefully position the cupcake wheels in the cake. (NOTE: your fingers will get gooey with this step, it is inevitable. Don't worry because you can touch up the frosting later and sprinkle on some more sprinkles) Fill in any extra chocolate icing needed to cover up the exposed cupcake.
Finally with an icing decorator with a flat tip you can apply white icing in strips to create Lightning's eye windshield, side windows, and mouth. I also used it to make a "3" in the back.
Next I used a pointed tip to create the lightning bolts, headlights, and Happy Birthday in the back with yellow icing.
Finally, I used two blue plain M&Ms to create Lighting's bright blue eyes and dotted some chocolate icing in the middle to bring him alive.
Everyone loved this little guy and every part of him was edible. I spent only $2 on the two cake mixes and $3 on the icing. I had the sprinkles at home along with the food coloring. So it only cost me $5 to make an amazing 3D cake that could have cost a lot more at a cake shop. We served well over 20 people with this cake plus had extra cupcakes from making the "wheels". I hope you can enjoy re-creating him yourself for your special Lightning McQueen fan!!!