How to Make a Rainbow Cake

This past weekend I made a 2nd birthday cake for the nephew of one of my best friends. The decorations they wanted were fairly simple – a lot of bright, primary colors (much like what was used on the clown smash cake), with a train track running around the outside of the cake. The train set on the cake was used on birthday cakes when the little boy’s mom and aunt were little, and they wanted to continue the tradition. The track ended up being the perfect size to set the train on! But the real magic of this cake was on the inside… a rainbow cake!

I have made a few children’s cakes like this before, and have been asked how it’s done, so I thought it was high time that I put together a tutorial for you. It’s such a fun, whimsical way to brighten up a child’s birthday cake, and is incredibly easy to do. Below are the step-by-step instructions with photos. Have fun!

First up, you’ll want to have your favorite white cake recipe handy. My personal favorite is the Perfect Party Cake, but any of your favorite recipes will work, and you could always use a box mix too, if you prefer.

A quick note on cake recipes… I always use this Cake Batter Chart from Wilton when baking cakes that I’m going to decorate. They call for more batter than you would typically use, but the cakes bake up nice and tall and, once leveled, create wonderfully high layers. Not only is more cake better for everyone, but you have more space on the sides for decorating! To give you some perspective, a typical recipe for a 2-layer 9″ cake yields anywhere from 4 to 5 cups of batter.

Now, grease and flour those cake pans!

Next, mix up the batter for your cake and get 6 bowls (or your fanciest plasticware) ready…

You want to evenly divide your cake batter between the 6 bowls/containers. The best way to do this is to measure the batter into a large (4-cup) measuring cup (might have to do this two or three times) or to weigh the batter, and then do a quick “divided by 6” to get the amount you should be scooping into each container. This is probably the hardest part of the whole process ;-)

Now, round up your food coloring – liquid or gels. A lot of people have said they have great success with the AmeriColor gels, but I still had some liquid food coloring from other recipes to use up, so I went that route.

Time to color away! You’ll want to make the fun rainbow colors, naturally: red, orange, yellow, green, blue and purple. If you’re using the little 4-color kit like me, just combine red + yellow for orange, yellow + blue for green, and red + blue for purple.

Use as much as needed to get the color hue you’re going for. (Alternately, you could really do this for any color combinations you’d like. You can keep half plain white and the other half brown to do a zebra. Reader Julie on Facebook mentioned she saw a cake like this with varying shades of pink, and you could definitely do that as well.)

Now, we’re ready to load up the cake pans. You have two options here:

Option #1: You can make one cake layer red, orange and yellow, and make the second layer green, blue and purple. I chose to do the cake this way so that the individual colors really popped and you could see all of them really well.

Option #2: You can do all six colors in each layer. To do it this way, divide each color in half between the pans. So, half of the red would go in one pan, and the other half in the other pan, and then proceed the same way.

As I mentioned, I used Option #1, so that’s what you’ll see illustrated here. First, pour the red batter into the bottom of the cake pan.

Next, add the orange batter on top of the red. Slowly pour the batter into the middle of the pan. As you do so, the red layer below it will spread out.

Finally, pour the yellow batter in the same way you poured the orange.

Repeat the process in the other cake pan, starting with the purple, and then adding the blue and green.

Bake those babies up!

Once the cakes have completely cooled, I like to wrap them in plastic wrap and refrigerate them for at least an hour. I find that it’s much easier to level cold cakes then room temperature ones. They are firmer and don’t crumble, making for a cleaner cut.

I use this Wilton Cake Leveler to level my cakes. It’s super cheap (less than $5 – you can find them at a place like Michael’s), and makes it incredibly easy to make sure the cakes are sliced evenly and cleanly.

Here’s what the tops of the cakes looked like after they were leveled… so colorful!

At this point, I went ahead and filled the cake and then decorated it.

I received a couple of questions on how to make the train tracks on top of the cake, so I’ve included that short description below as well.

How to Make Train Tracks

My friend told me that the tracks needed to be ¾-inch wide in order to accommodate the plastic trains that they wanted to decorate the cake with. I used brown fondant rolled out to about 1/16-inch thickness, and then cut a long strip ¾-inch wide. From there, I cut across the strip in ¼-inch increments until I had as many “tracks” as I needed.

Once I was ready, I spaced them evenly around the cake. To make the rails, I used a #2 decorating tip with black icing.

And here was the finished cake, before it went out for delivery and got adorned with the adorable train set that you saw in the first picture.

(Thank you to my friend Renee for snapping those pictures for me so I would have photos of the cake with the train on it, and the inside of the cake once it was cut!)

I hope you enjoyed the tutorial!