My daughter's birthday comes very quickly after Christmas, so its hard to muster up the energy to plan her party, let along her birthday cake. Well, its hard for me. My daughter had a million ideas. This year she turned five and was extremely insistent that I step up and pull all the details together. The party was easy enough (ballerina princess party, of course) but for the cake she wanted a rainbow cake. No problem enough I thought, I have made a couple before.
Except, she wanted a chocolate rainbow cake. She was very insistent. I tried to explain that I couldn't make a chocolate rainbow cake. She wouldn't hear of it. Chocolate, had to be. So, I started thinking – could I make a chocolate rainbow cake? I dismissed a velvet cake because I didn't think the colors would be vibrant enough and I didn't think my daughter would believe me when I said it was chocolate. What I could do was make the rainbow with the buttercream frosting in between the layers.
After that the cake was simple enough. I made a fudgy chocolate cake (which in retrospect was a little crumbly for this but still tasted great). I worked out how many layers I would need – I ended up with eight layers of cake, seven layers of icing. Cutting the layers is actually simpler than you would think. The recipe makes two layers in 9" pans. You cut each layer in half and then cut each piece in half and voila! Eight layers. It helps to have a long knife and to refrigerate the cake before you cut it. I made the cake the day before and frosted it the morning of.
I underestimated how much frosting I would need. I ran out before I was finished and because I was frosting it the morning of – I didn't have time to make more. It became a poorly executed naked cake instead of the cloud design I was planning. Which was fine, I was disappointed, but the birthday girl loved it. Next time (because I absolutely need more chocolate rainbow cakes in my life) I will make two regular size batches of frosting instead of an extra-large batch. An extra-large batch is pretty much the most I can fit in my mixer anyway and truthfully, it's pushing it a bit. So, two batches will be better all the way around.
To make the colors I separated out the frosting into individual bowls and made all the colors before I started. I used two scoops from my #12 cookie scoop for each layer and that was just enough to cover with enough that you could see once the cake was cut. Gel food coloring seems to work best, so you don't add too much liquid to the frosting. I admit that I have all the colors, so I don't need to mix them. It's easier and the colors turn out better that way – especially purple. Purple can turn out sort of mauve in my experience if you don't have purple food coloring.
In the end, the kids were impressed with the rainbow layers and the birthday girl was thrilled with her chocolate rainbow cake. Once I worked it out, it wasn't very hard to make. My five year-old asks for a Chocolate Rainbow cake? – Challenge Met.
Chocolate Rainbow Cake
Chocolate Cake with rainbow layered buttercream.
- 1 1/4 cups (115g) unsweetened cocoa (dutch processed)
- 2 cups boiling water
- 4 cups (400g) cake flour
- 3 teaspoons baking powder
- 1 teaspoon baking soda
- 1 teaspoon salt
- 1 1/3 cups (2 sticks, 6 Tbsp or 310g) unsalted butter, room temp
- 2 2/3 cups (578g) light brown sugar
- 4 large eggs
- 2 teaspoons vanilla bean paste (or extract)
1. Preheat oven to 350°F. Grease two 9" by 2" cake pans, line the bottoms with parchment and grease the parchment.
2. In a medium bowl, whisk together the cocoa and the boiling water until smooth. Allow the mixture to cool to room temperature.
3. In a large bowl, sift together the flour, baking powder, baking soda, and salt. Set aside.
4. In the bowl of a stand mixer (or a large bowl with an electric mixer) beat the butter and brown sugar until light and fluffy. Add the eggs one at a time, scraping down the bowl between additions.
5. Beat in the cocoa mixture and the vanilla. Add in the flour mixture in two additions until just combined.
6. Divide the batter between the pans and smooth the surface with a spatula. Bake in the middle of the oven for about 40 to 45 minutes or until a tester inserted near the middle comes out clean and the cake springs back with lightly pressed in the center.
7. Let the cake layers cool in the pans on racks for about 10 minutes and then invert layers onto racks (you may need to run a spatula around the edges first). Carefully peel of the parchment off the bottoms and reinvert so that the cake is upright. Allow to cool completely before frosting. Cake layers may be made 1-2 days ahead and kept, wrapped well in plastic wrap at room temperature or up to 5 days in the refrigerator.Chilling the layers also makes them easier to cut later.
8. Time to put the cake together. Make two batches of Swiss Meringue Buttercream (Recipe follows). Using a #12 cookie scoop, separate out six portions of buttercream, 2 scoops in each portion (about 2/3 cup each). Set aside the remaining buttercream. Using gel food coloring - color each portion of buttercream a color of the rainbow. You'll have a portion for indigo, I'm a geek that way.
9. Level your cake layers so they are flat and then cut them into 4 layers each. This is easier than it sounds. Cut them first in half and then cut each half in half and you are done.
10. Start layering your cake. Place your bottom layer on a plate or 10" cake round and spread your bottom color, there should be just enough to create a thin even layer. I tend to make my layers on the thicker side so you might have a little extra. I started my rainbow with purple on the bottom but it can go either way. Repeat with each layer until you use all your colors and you put the top layer on top.
11. Cover your cake in a crumb coat and put it in the fridge to chill for 30 min. Finish your cake with the remaining frosting.
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Swiss Meringue Buttercream
European style, meringue based buttercream. Makes a little more than 4 cups.
- 5 large egg whites (room temp)
- 1 cup (200g) granulated sugar
- 1/8 teaspoon (generous pinch) salt
- 3 sticks (1 1/2 cups) unsalted butter (softened)
- 2 teaspoons vanilla extract
1. Combine egg whites, sugar, and salt in the heatproof bowl of a standing mixer (or a medium bowl if you are going to use a hand mixer to whip later). Set the bowl over a medium pan of simmering water, make sure the bowl doesn't touch the water.
2. Whisk continuously until the sugar is completely dissolved and the mixture reaches 160°on a candy (or instant read) thermometer, about five minutes. Scrape down the sides every now and then with a rubber spatula to get all of the sugar from the sides of the bowl. The mixture should feel completely smooth to the touch and quite hot.
3. Once you reach 160°, immediately move the bowl to the stand mixer, fitted with the whisk attachment. Begin on low speed and gradually increase the speed until you are at medium high speed. Whisk until you have stiff peaks, about 10 minutes. It looks a lot like marshmallow at this point. The bottom of the bowl should be room temperature and the egg mixture should be cool.
4. Reduce the mixer speed to low and begin adding butter, a tablespoon or two at a time. The butter should give a bit when pressed but not so soft it looses its form. Make sure the butter is fully incorporated before adding more. Occasionally stop to scrape down the sides and bottom of the bowl. As you add the butter, the meringue will deflate - don't panic, its all part of the process.
5. Once all of the butter has been incorporated, whisk in the vanilla. Switch to the paddle attachment and beat on low speed for a couple minutes to smooth it out and eliminate all air bubbles.
Leave buttercream at room temperature if using that day. It can also be refrigerated or frozen, but be sure to bring it to room temperature and then rewhip for a couple minutes before using. You must bring it back to room temperature first, however, or the buttercream will seperate. Buttercream will keep 2 days at room temperature, 10 days or so well wrapped in the fridge, and a couple of months in the freezer.