This cake took 4 days, but only because I wanted it to "work" with the slanted stripes inside that look like construction tape, so I wasn't taking any chances. You could probably do it over 2 days, since you need time to freeze the layers.
A pretty picture of the outside.
That was the easy part, decorating it with smashed Oreos as "dirt" and small construction machines that tied into the entire Construction Machine Birthday Party theme.
Now for the hard part, getting slanted layers.
That's me proudly holding up the first slice.
Usually I'm all about making everythign from scratch, but I figured I was going to so much trouble with this cake that I wanted to be sure the texture would work.
Bake two (2) 2-layer cakes in 9 inch rounds. You will end up with 2 yellow rounds and 2 chocolate rounds.
Wrap each layer and put them in the freezer so they wil be easier to work with.
After they are frozen take them out and set them on your work surface. I would recommend a rotating cake stand, but I used a large platter and it worked fine.
Level your cakes if they are too domes on the top, mine were pretty flat so I skipped this step.
Place your long serrated knife (bread knife) about half an inch in fron the side of the cake. Angle the knife, about 45 degrees, and start cutting through the cake, turning and cutting until you get all the way around.
Now you can separate the two pieces.
You repeat this step except closer to the center of the cake. Once you do one of the rounds, you can take the inside pieces and set them upside-down on the other layers to use as a guide.
If I were being a perfectionist about it, I would "trace" a round bowl onto the top of the cakes so that they were perfect, but the frosting does a pretty good job binding them together.
Now alternate your pieces. So chocolate-yellow-chocolate for two cakes, and yellow-chocolate-yellow for two.
Wrap these "new" cakes individually in Saran and place them in the freezer again.
When they come out of the freezer (I waited a day, but it could probably be an hour or two), stack them on top of each other, alternating outside color.
Make sure to frost in between the layers to make them stick together.
Now frost the top and sides of the cake.
After the crumb coat, which is just the first coat of frosting, I put the whole thing in the freezer to make it easier to work with on P-day (party-day).
My lovely friend Jill got me cake stencils for my birthday, so I decided to try them out on this cake. DO NOT do that. Do not try something totally new and different for making the cake, a construction technique, new frosting, decorating AND stenciling. Bad idea. The first time the powdered sugar just went everywhere.
I frosted over it.
The second time it worked, see how I'm holding the stencil taut? That's so it doesn't stick to the frosting.
I could pretend that was the end, but once it went into the fridge to stay cool the powdered sugar kind of disappeared. So that's why you won't really see the "Happy Birthday" on the final pictures:) Just keeping it real.
My daughter smashes the chocolate cookies (Trader Joe's Joe-Joe's or Oreos work well) inside a zip-top bag, with teh frosting container. At least this way I wasn't worried about her accidentally hurting the marble counters!
The finished product. This is where all my mommy-training was put to the test since my kids wanted to place the decorations.
I let them.

See how the "3" is falling off a bit? I decided that Pinterest and the blogosphere weren't being served any better by me being a control freak about a cake.
Delicious and adorable! Just like my children!
I got the idea from Pinterest, thankfully there was a picture tutorial for a slanted stripe cake.
Jessica
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I link to these awesome parties:
Sunday: I Heart Naptime, Nifty Thrifty Things, It's Overflowing Monday: Delectable Home, C.R.A.F.T. DIY Showoff, Between Naps on the Porch, Thrifty Decor Chick, Debbie Doo's, Home Stories A to Z, Evolution of Style Tuesday: Coastal Charm, Nest for Less, Tip Junkie, My Uncommon Slice of Suburbia, A Bowl Full of Lemons, Get Your Craft On, Kurtz Corner, Centsational Girl , Primitive and Proper Wednesday: Savvy Southern Style, Organize and Decorate, Mommy Solutions, Power of Paint, Newlyweds Recipe Linky, Southern Lovely , Home Happy Home, Crafty Sasse Wednesday, Gingersnap Crafts, A Crafty Soiree Thursday: The Shabby Creek Cottage, Made in a Day, House of Hepworths, the 36th Avenue, Crafty, Scrappy, Happy, 52 Mantels Friday: Making Lemonade, Blissful and Domestic, One Artsy Mama, Serenity Now, Tatertots and Jello, The Shabby Nest, Thirty Handmade Days, Addicted 2 Decorating, Funky Junk Interiors, Financial Friday, Furniture Friday, At the Picket Fence, The Rooster and the Hen, Classy Clutter
The Pinterest Challenge by Young House Love, Bower Power, Centsational Girl and Ten June