So, this is my first post since April. That is a long time. So this is a celebrations post, and what better recipe to celebrate with than a Rainbow Cake!
We are celebrating my first post in over 8 months, we are celebrating that I now have 325 Facebook followers (even with my crazy sometimes-on, sometimes-off posting), we are celebrating that after 16 (often torturous) months of construction and near disasters, our new house is finished and we finally moved in right before Thanksgiving, we are celebrating that our horses are finally all with us on the same property, we are celebrating that after years, our two dogs are finally starting to have manners at the door (good grief), we are celebrating my 40th birthday (in October), we are celebrating that my oldest is a senior and is planning on attending Utah State in the fall (*sniff!*), we are celebrating that my youngest is in 1st grade (*double-sniff!*), we are celebrating that my husband has a job after his company had yet another round of lay-offs, we are celebrating that tomorrow is Christmas (squee!), and we are celebrating that a new year is just around the corner, with all the hope and promises and amazing things that are waiting for us.
This Rainbow Cake is one of the coolest things I've ever baked. So unassuming on the outside, and then, Wham-O! Color on the inside! So cool.
There are a couple recipes for Rainbow Cakes floating around the internet. When I read through the comments I saw that more people than not had trouble with the icing. I think it's because it's the type of buttercream that is mostly butter and requires just the right amount of whipping and just the right temperature. So for this recipe, not only did I make the cake high-altitude friendly, but I used my regular vanilla buttercream, which always works and is 0% tricky.
Another issue people commented on was the flavor of the cake. Because it's a white cake (so no egg yolks) the flavor is very light. If you want, you can add some orange or lemon extract to give it more flavor. I'd say 1 to 1 1/2 teaspoons. But I think using a good quality vanilla is a really good start.
A couple of notes: *If you want a white cake that's not a Rainbow Cake, this recipe will make 2 9-inch cake layers (make sure to use 2-inch high pans). *While I formulated this cake for high altitude, a friend made it in Alaska and it turned out fine. *This cake is 6 layers high, which means it is tricky to frost because the layers want to slide all over when you start putting pressure on the sides with your icing spatula. This is why I ended up using my giant star decorating tip to put the frosting on in swirls; it was much easier because it didn't make the layers slide around. This technique does use more frosting, though, so I ended up using a bigger batch of my favorite vanilla buttercream.
for the white cake:
2 sticks salted butter, room temperature
2 cups + 1 tablespoons sugar
10 egg whites, room temperature (you can use the egg whites that come in a carton)
4 teaspoons vanilla
14 oz all-purpose flour, sifted
2 1/2 teaspoons baking powder
1/2 teaspoon salt
1 cup + 2 tablespoons buttermilk (at lower altitudes you can use whole milk)
1. Heat your oven to 350 and grease and flour 2 9-in round pans. Line the bottom with parchment paper (don't skip this part).
2. Sift together the flour, baking powder and salt. Set aside.
3. Cream together the butter and sugar until fluffy. Add half the egg whites and mix well on medium speed, scrape the sides of the bowl. Add the remaining egg whites and mix well on medium speed, then scrape the sides of the bowl. Add the vanilla and mix well.
4. Add 1/3 of the flour mixture and mix well. Add 1/2 of the buttermilk (or whole milk) and mix well. Scrape the sides of the bowl. Add another 1/3 of the flour mixture and mix well. Add the remaining buttermilk and mix well. Scrape the sides of the bowl. Add the remaining flour mixture and mix well.
5. Divide the batter evenly into 6 bowls. I found it was easiest to use my muffin scoop to divide it up (1 scoop in each bowl, another scoop in each bowl, etc.). Use gel food coloring (not liquid--it will thin the batter) to color the batter rainbow colors. Pick 2 of the colors and spread one each in the bottom of each of the prepared pans. Bake for 8-10 minutes or until the cake springs back when touched. Let the cakes cool for about 5 minutes, then turn them out of the pans onto cooling racks and peel off the parchment. Wipe out the pans, re-grease and flour and line with parchment, and then repeat with the remaining colors until you have all 6 colors baked.
for the icing:
1 1/2 cups butter, softened
1 cup vegetable shortening
1 tablespoon vanilla
3 lb powdered sugar
1/3-1/2 cup milk or cream
With an electric mixer (stand mixer or hand mixer), cream together the butter and shortening; scrape the sides and bottom of the bowl well. Add the vanilla and mix well. Add the powdered sugar and mix on low until the mixture is very dry and crumbly; scrape the sides and bottom of the bowl well. With the mixer on low, add the milk, 1 tablespoon at a time, until the frosting is a nice, spreadable consistency. Wait about 5 minutes before you use the frosting to see if you need to add a little more milk to get the consistency you want.
Makes about 9 cups frosting.
to assemble the cake:
Put the color cake you want to be on the bottom of your cake on your serving plate. Spread the top with 1/3-1/2 cup frosting. Put the next color on top, spread with another 1/3-1/2 cup frosting. Repeat with the remaining colors until you've got them stacked.
Important: The cakes will want to droop at the edges. This is partly because they aren't perfectly flat, and partly because there are so many. The drooping will get more pronounced with each layer you add. To help with the drooping, when you spread the top of the layers with the frosting leave a little extra frosting at the edges so when you put the next layer on it's as flat as possible. Also important, when stacking the layers try to make them as straight and lined-up as possible.
When you've got all the layers stacked and straight, use the rest of the frosting to frost the top and sides. It's a little easier to do the sides first so you can touch the top with your fingers to keep the cake steady. I used a tip #1M (a huge star tip) to make big swirls. It was easier to use the decorating tip because the 6 layers wanted to slip around when I put pressure on the sides with the frosting spatula.