First spotted this cake on Whisk Kid - of course I bookmarked it and knew that this, this was going to be Bear's birthday cake. How could it not be? It's unbelievable!
Tinting the cake batter was no big thing, once I did a bit of research and decided to shell out $16.00 for a box of fancy Wilton food coloring gel. That stuff is incredible. The colors, as you can see, were intense and true - although the picture makes the red and orange look similar, in reality they were obviously different.
In my opinion, the most difficult and labor intensive part of this whole thing was the buttercream icing. She's a fickle bitch. I went with a recipe I've never tried before - but it's Bon Appétit, it'll work, right? Remind me (again, please) that trying out a new recipe on something that has to be seen by other people is never a good idea.
While I was beating the egg whites and sugar for the second batch (with a hand mixer - I really, really need a stand mixer!!!), my other hand was stirring the sugar syrup on the stove. The thing about sugar is that when it starts to caramelize, it happens fast. I did take the pan off the heat before the browning started - but as I was pouring it (in a slow, steady stream so as not to cook the egg whites), the residual heat from the pan nearly caramelized the sugar! In layman's terms: almost caramelized sugar syrup = golden sugar syrup = pinkish buttercream.
I figured I had this recipe whipped by now, and sure enough, the third batch turned out beautifully - silky smooth, and it melted on the tongue. I'd run out of butter and eggs so I decided I'd layer as much of the cake as I could and finish the rest the next day.
One more batch of buttercream the next morning (yeah, I've got that recipe wrapped around my little finger now), and I came to a brilliant conclusion for the pink buttercream: crumb coat!! It wouldn't be noticeable to anyone but me, and that would leave more of the bright white perfect buttercream to frost the rest of the cake with.
When I forced myself to quit fussing with the icing, laid down my spatula and called it good - I was sort of shocked at the sheer size of the finished cake. Sure, the six cake layers are quite thin - but pile icing in between each one of them, frost the top and sides of the cake and goodness gracious you've got yourself, well, an Epic Rainbow Cake.
It went over well at the party though. I was so nervous cutting into it - my hands were shaking. But when I slid that first slice out and saw that hey! It worked! And everyone gasped and oohed and aahed...I was happy. Bear loved the icing.
Go ahead, make the cake. It's a showstopper, for sure. However - don't make it for a small gathering. Because of all of that gloriously rich icing, even the thinnest of slices may not get finished. It's a terribly filling cake - I have a quarter of it in the freezer yet.
The buttercream recipe I used isn't terribly sweet, which in my opinion is a good thing when you're using this much of it.
Super Epic Rainbow Cake
Makes one (gigantic) 9 inch six layered cake
1 cup butter, room temperature
2 1/3 cups sugar
5 egg whites, room temperature
2 teaspoons vanilla
3 cups flour
4 teaspoons baking powder
1/2 teaspoon salt
1 1/2 cups milk, warmed to room temperature
red, orange, yellow, green, blue and purple food coloring
Preheat oven to 350F. Grease your 9 inch cake pans (I have 2 commercial pans, I just kept washing, re greasing and re lining) and line with parchment on the bottoms.
Sift together the flour, baking powder and salt. Set aside.
Cream the butter and sugar, then add the eggs whites a little at a time. Add vanilla and mix till blended. Alternating between wet and dry, add the milk and flour mixture.
Divide the batter amongst 6 bowls - Kaitlin suggested doing this by weight, but I just used a 1 cup measuring cup to start and as the batter decreased, I used a 1/4 cup measure till all the batter was gone. Whisk a fair amount of each food color into each bowl, pour into your prepared pans and bake for approximately 15 minutes each.
Let the baked cakes cool in the pan for a few minutes, then finish cooling on a rack.
Basic Vanilla Buttercream
5 large egg whites
1 2/3 cups sugar, divided
1 teaspoon vanilla
1/3 cup water
1 pound unsalted butter, diced, room temperature
Note - it is indescribably important to have each and every one of your ingredients at room temperature or your buttercream will fail. That's pretty much guaranteed. Trust me.
Combine egg whites and 1/3 cup of sugar in a large bowl using a mixer. Add vanilla.
Combine remaining 1 1/3 cups sugar and 1/3 cup water in a medium saucepan; stir over medium heat until sugar dissolves and syrup is bubbling.
Meanwhile, beat egg white mixture on medium speed until very soft peaks form.
Increase mixer speed to high and slowly pour hot syrup down the side of the bowl into egg white mixture in a slow, steady stream. Beat until this meringue forms stiff peaks. Allow meringue to cool in the bowl until lukewarm. Do not beat to cool.
Once lukewarm, start beating meringue on medium speed. Gradually add butter, a few tablespoons at a time, beating constantly till each addition is absorbed before adding next. Continue beating until buttercream is smooth.
If buttercream looks 'broken' or curdled, you can try placing the bowl of buttercream over medium heat on a stove burner and whisk for 5-10 seconds to warm slightly, then remove from heat and whisk vigorously or beat again on medium speed. Repeat this process until buttercream becomes smooth. Keep in mind, this may not work and it might not be salvageable.
You will be able to tell when the buttercream is starting to come together by listening to your mixer - all of a sudden it will start to sound as though it is working harder, and then the buttercream will come together quickly.