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How to Make an Ombré Rainbow Cake

That tastes just as good as it looks.

In the days leading up to my friend Rachel's baby shower, I had every intention of baking adorable baby bottle-shaped cookies, and went so far as to buy a shaped cutter. But as the party got closer, I realized the thought of making and decorating cookies was only adding stress, not excitement to the preparation process. On a last-minute whim, I reached out to Danielle who made the most beautiful cookies for the party. I'm excited for her to share more delectable and beautiful desserts—this time in the form of a Hawaii-inspired rainbow cake, which feels perfectly timed not just for our own Hawaiian vacation, but for Pride Month! -Emily

I recently got back from a trip to the Hawaiian island of Kauai where a beautiful rainbow is not an uncommon sight, and definitely something I could get used to seeing every day (in addition to the endless waterfalls, juice huts, shaved ice, and cats everywhere). I often find cake decoration inspiration in nature—it translates well as nature is imperfect and asymmetrical, just like cake decorating. This rainbow cake looks impressive, but is truly something even a beginner baker can manage. As such, it’s important to know the basic steps, but there is no right or wrong way to reach the finished product. Just add a few extra sprinkles or garnishes can make it your own (and disguise any flaws). Read on for my tips for creating a rainbow cake!


Ombré Rainbow Cake


Begin with four eight-inch cake rounds and bake a classic birthday cake, either from Emily's favorite recipe or my personal favorite. It should be baked in two 8"-round cake pans and once it's completely cooled, cut in half horizontally to make 4 cake layers. 

Next, prepare 15 cups of a Swiss meringue buttercream (I use this recipe and multiply it by three).


To prepare your cake, fill a piping bag with frosting and pipe about one tablespoon of buttercream onto the board or stand (or turntable if you have it) and then place the first cake round on top of that. This keeps the cake from sliding off the stand. Then, pipe an even circle covering the top surface of the cake. (I like to pipe a layer that is about 1/2" thick but if you like more frosting in-between your cake layers, feel free to pipe more!) Stack and repeat the process with the remaining three cake rounds. Place the cake in the fridge until chilled and firm—at least 30 minutes—so that the cake tiers don't move around during the next step. 


Remove the cake from the fridge and pipe an equal amount of buttercream on top of the cake and around the sides. Again, the amount is not an exact science, but you want the same amount on sides and top for an even-looking cake (and you can easily remove some if you accidentally add too much to any one side) and to reserve about two-thirds of frosting for the final coat. Smooth the buttercream out with a large offset spatula and remove any excess to a bowl. This is a base crumb coat, or a thick layer of frosting that keeps cake crumbs from showing on the final coat of frosting, which is all to say it does not need to look perfect. Return to the fridge for another 30 minutes to chill.


While the cake is chilling, color the rest of your frosting using a gel food coloring. Divide the remaining frosting evenly into as many bowls as there are colors you want to create, dedicating one bowl for each color (I had six). Add coloring one drop at a time (I like to use this coloring set) and whisk to incorporate, adding more as needed to achieve the desired hue. Pinks tend to be very strong and only need 1 to 2 drops, while yellows and greens need more drops to look saturated. Place each colored frosting in a separate piping bag.


Remove the cake from the fridge and evenly pipe lines of frosting around the cake starting at the base and working your way up (if you want to make frosting a cake more foolproof, invest in a turntable like this one that comes with all the tools). Try to hold the piping bag at a 90° angle to the cake, and move in as continuous a motion as possible (moving side-to-side or up and down will cause the lines to blur together). The general coloring of a rainbow would go from ROYGBIV, but feel free to mix it up if you like! 


With a large offset spatula and icing smoother, work your way around the cake, smoothing out the sides as you go. Remove any excess frosting to a bowl. Keep the tools at a 90° angle and the bottom at the base of the cake. Don’t move up and down or the colors will start to blend together. Once the sides are smooth, work on smoothing out the top of the cake. Keep the icing smoother at a 45° angle and scrape towards the center of the cake, removing any excess frosting. 


Fill piping bags with different sized star tips and colors. Add piped stars and rosettes to the top and sides of cake. Add multicolor sprinkles, sparingly, as garnish. 

And now the best part: Serve the cake at room temperature or store it in the fridge and remove 1 1/2 to 2 hours before serving. Enjoy! 


Thank you, Danielle, for sharing this fun and beautiful cake! 

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