If you’re looking to impress, a rainbow cake is just the thing. But as impressive as they are, did you know they’re also very easy to make? Time consuming, yes, difficult, no. My youngest daughter’s birthday is this month, and somehow she’s getting four cakes out of it. For her actual birthday I decided to knock her cute little socks off and make a rainbow cake. She literally gasped when I handed her the first slice. Mission accomplished. Read on to learn an easy rainbow cake recipe and how to decorate your masterpiece.
You can use any light colored cake for a rainbow cake. I usually use my favorite Nick Malgieri vanilla cake recipe, but you can use anything as long as it’s white/cream colored. You can even use a coconut or lemon cake. This is the third cake I’ve made in as many days, so I took the easy route and went with a vanilla cake mix.
Depending on how big you want your cake, you may need to double up your recipe. I used 6 inch round pans so I was able to get thicker layers with just one batch. If you’re using 9 inch pans you may want to double up the recipe. If the cakes dome up you’ll need to trim them, so a bit of extra batter is a good thing. I had very thin layers and they didn’t dome much at all.
Once your cake batter is made, you’ll want to split it into six different bowls. You can just eyeball the batter to determine if it’s fairly equal, or if you’re really technical you can weight the bowls to make sure they have the same amount.
Once you have six equal bowls of batter, it’s time to add the food coloring. I like gel food coloring, and I find a little goes a long way so start with just a dab. Rather than squeeze it out of the bottle directly into the batter I use a toothpick to add a little at a time. Stir until the color is uniform, add more if needed. Once all your bowls are colored, it’s baking time.
You probably don’t have six pans of the same size, but if you do this will go a lot quicker. I have three six inch rounds so I only had to bake in two batches. If you have friendly neighbors go borrow their cake pans.
Once you have the batter in each cake pan it will probably seem like there is barely any in, but don’t worry, the cakes will rise well. As long as there is cake batter covering the entire base it will be fine. Mixing in the food coloring probably added quite a bit of air to your batter so before putting them in the oven give each pan a smack on your counter. This will pop most of the air bubbles and prevent doming.
Keep a close eye on your layers, since you’ve split them up into six batches they’ll bake a lot faster. My six inch rounds took about 12 minutes each. Once they are done let them cool and then run a small knife around the edge to loosen from the pan. Gently tap the cakes out and let them cool completely on a cooling rack.
Once they are cool trim off the tops if any of the layers domed. The flatter your layers the easier it is to frost and get an even cake.
Getting Your Frosting Ready
You can use any white colored frosting for a rainbow layer cake. For my cakes I usually use my favorite American buttercream. You can learn how to make it in this post.
If you’re just going to use one color of frosting on your cake one batch of frosting should do it. However, if you want to do a rainbow frosting you will need another half batch. If you aren’t sure how much you’ll need just leave your butter out so you can whip up extra frosting if needed.
Once your frosting is made, it’s time to crumb coat. Check out this post for details on how to do a crumb coat to keep pesky crumbs trapped. If you’re using one color for the frosting you can color your frosting and then crumb coat, if you’re doing rainbow frosting just leave it white for now.
Start stacking the layers with about 1/4 cup of frosting between each (a little more if you’re using 9 inch rounds). My oldest daughter was close by making sure I didn’t screw up the rainbow order, but if you don’t have astute helper nearby here is the rainbow order, starting at the bottom:
Apparently they teach that in school. I must have been sick that day.
Once the layers are put together add your crumb coat to the outside of the cake. If your cake isn’t perfectly flat and even, I like to add more frosting then just a thin layer on top to even it out. You can add more frosting later if it’s still lopsided.
Your cake is probably quite tall by now and a bit wobbly. Put your cake in the fridge for at least 30 minutes at this point. This will not only help the crumb coat harden faster, but it will make your cake more stable while you frost.
In the meantime you can color your frosting. Split your frosting into seven bowls; one for each rainbow color, and leave one white for the top of your cake. Again, start with less, and add more if needed. You don’t need to use your mixer to add the color, you can just mix it up in the bowl. Once the frosting is done, you will need to put each color into it’s own piping bag. If you don’t have six piping bags you can use a Ziploc, but if you’re using a tip with them this can get really messy.
Frost Like a Boss
Your cake is crumb coated and cooled. Your frosting is made and in six piping bags. Now let’s get our frost on!
If you have a cake turn table this makes frosting easier, but it’s not necessary. Start with purple on the bottom and pipe two to three layers of frosting around the entire edge of the cake. I used a small closed star tip for this, but you can use whatever tip you like if you’re going to smooth it all out anyways. Piping it just makes it way easier to get frosting on the cake evenly.
Add the next layer (blue), and so on. Each of the layers should touch, and it’s ok if they get on top of each other a bit. Once you smooth the frosting out it won’t be noticeable. You can use the same tip, and just wash it out before attaching it to the next piping bag, or just use a different tip if you’re going to smooth it out.
Once you’re done all the way to the top, get out your large offset spatula. Smooth the frosting out as you spin the cake, making sure the cake is completely covered. Don’t worry about this being perfect, ridges and ripples are a cool effect. Keep smoothing it out until your happy though.
When you’re happy with the side of the cake, add some of the white frosting to the top and use it to even it out. Bring the frosting all the way to the side where it will meet the red. I use a small offset spatula to clean up the sides.
You can leave the cake just like this or add some sprinkles on top. I love these nonpareil rainbow sprinkles, you can add just a few or coat the entire top like I did.
It’s All Sunshine and Rainbows
That’s it, you’re done! Just wait until you cut into your rainbow cake, it’s truly magical. Well, maybe that’s taking it a bit far, but this is one impressive cake. As I said before, it does take some time to put together, but you definitely don’t need to be a pastry chef to pull it off.
Just to recap, for this rainbow layer cake you will need:
- 1-2 vanilla or white cake mixes
- 1-2 batches of American buttercream frosting
- six piping bags
- at least one piping tip
- six bottles of gel food coloring (purple, blue, green, yellow, orange, red)
- large offset spatula
- small offset spatula
I hope you found this tutorial helpful and easy to follow. If you have any questions or would like to share your own tips for making rainbow cakes, please leave a comment below!