The Cake Therapist's Rainbow Cake

I have a thing for rainbow cake. It's an American layer cake gone happy, happy, happy with color. There’s something about a rainbow cake that just makes me smile. Every colorful layer seems to suggest a different story. 
When I was working on The Cake Therapist, my debut novel, I wanted a signature cake for the main character. Pastry chef Claire "Neely" O'Neil Davis can see flavors like a rainbow. Her bakery's name is "Rainbow Cake," and she highlights a different color and flavor pairing every month.  So her bakery is colorful. And her specialty is individual rainbow cakes with robin's egg blue frosting.
At home, you can make a rainbow cake large or individual-sized , as you can see in this previous blog post. You can go more vividly colored or more pastel. You can do an ombre effect, dark to light layers in the same color family, such as purple to lavender to purplish pink to raspberry to pale pink to white. Making a rainbow cake taps into your inner colorist.

For the cover of The Cake Therapist, the rainbow cake is what pastry chefs call "naked," meaning without frosting on the sides of top. If you want to do that, I'd use a white cake that doesn't brown at the edges. This cake recipe, below, is rich with butter and whole eggs, turning the batter more of a creamy color that does brown at the edges.

Here is that batter turned into a four-layer rainbow cake I whipped up in my kitchen for Bake Happy. You can find cake buntings (that you can use again and again) on Etsy.

My new favorite way to make one is in five thin layers, each a different pastel, with robin's egg blue or pale turquoise buttercream frosting to finish. Maybe a generous sprinkling of colored sprinkles.
Here's a taste of Neely's famous rainbow cake that you can whip up for a special occasion, a birthday, or just because.

Neely’s Rainbow Cake

Adapted from a recipe in Bake Happy, this is the larger version of Neely's individual rainbow cakes that she makes at her fictional bakery in The Cake Therapist. The cake is rich, moist, comes out of the pans easily, and keeps well.  

Makes one 8-inch (5-layer) cake

Unsalted butter for the pans

11/2 cups (340 g) unsalted butter, at room temperature

3 cups (700 g) granulated sugar

3 large eggs, beaten

3 cups (248 g) sifted cake flour

2 teaspoons baking powder

1/2 teaspoon salt

11/2 cups (375 g) non-fat Greek yogurt, or full-fat dairy sour cream

11/2 teaspoons vanilla or almond extract or a combination

Gel food coloring, as desired

Preheat the oven to 350°F (180°C). Butter five (8-inch) cake pans and set aside.

In a large bowl, with an electric mixer on low speed, cream the butter and granulated sugar for 5 to 7 minutes or until the mixture is almost white. (Don't rush it. Beating air into the butter helps make a lighter cake.) 

Beat in the eggs, sour cream, and vanilla. Then beat in the flour, baking powder, and salt for 1 minute, scraping down the sides and the bottom of the bowl.

Set out 5 small bowls. In each small bowl, place about 1 generous cup of the batter and tint with food coloring to your desired color, such as Neely's pale yellow, green, coral, lavender, and pink. Keep in mind that the color will somewhat darken and brown during baking. Spoon the tinted cake batter into each prepared pan and smooth with a spatula or knife.

Bake for 20 to 23 minutes or until the cake comes away from the sides of the pan and is springy to the touch in the center. Let cool in the pan.  Invert the cakes onto a cooling rack and cool completely.

To assemble the cake, save the most domed layer for the top (or make Neely's pattern with lavender on the bottom, then coral, lime, yellow, and pink on top). Place the flattest layer on a serving plate and spread lightly--a skim coat-- with about 1/3 cup Robin’s Egg Blue Buttercream Frosting. Place another layer on top and frost lightly with another 1/3 cup frosting. Repeat with the third and fourth layers. Place the top layer. 

Using an offset spatula, frost the sides of the cake with half of the remaining frosting. Frost the top. If you like, decorate with colored sprinkles.

Robin’s Egg Blue Buttercream Frosting

You can never have too much of this silky-textured, light and airy frosting.

Makes about 5 cups 

5 large egg whites

1 cup plus 2 tablespoons (224 g) granulated sugar

1/4 teaspoon salt

2 cups/454 g unsalted butter, cut into tablespoons, at room temperature

11/2 teaspoons (7 ml) vanilla extract

Gel food coloring, such as Wilton’s Teal

Combine egg whites, sugar, and salt in the metal bowl set over a pan of simmering water so that the water does not touch the bottom of the bowl. Whisk the mixture by hand, constantly, until you can rub the warm mixture between your fingers and feel no sugar grit and an instant-read thermometer inserted in the mixture registers 160°F (75°C), about 5 minutes.

Mix  on medium-low speed with an electric mixer for several minutes until the sugared egg whites become foamy. Then increase the speed to medium-high and beat for several minutes until the egg whites are white and soft peaks form. Then increase the speed to high and whip until white, glossy, and stiff peaks form that just fall over at the tip when you test with your fingertip. Beating the egg whites should take a total of about 10 minutes.

Start adding the butter, a tablespoon at a time, beating on medium speed, and mixing well after each addition. When all the butter has been added, beat in the vanilla, food coloring, or any other flavoring until the buttercream is smooth and thick. Use right away or store, covered, in the refrigerator for up to 1 week. Let the frosting come to room temperature before using.

Recipe adapted from: