To form the rainbow in this cake I used the method shown here at Omnomiconwhich is very simple — separate your cake batter, color each section, then pour it into your cake pan one color on top of the next. The first time I saw this method was when my friend Maggi (hi Maggi!) made one a few years back. (update:Maggi’s cake is over here. Pretty.)
The trouble: Usually when one makes a cake like this you divide the batter into equal parts but that results in the color that went in first spreading out more as it cups around the colors that come on top. The result is that when you cut a slice of the final cake you get less of some colors and more of others.
Secret #1: Beneath the pile of gold coins are fragile bars, when the leprechaun approaches to grab the coins he’ll fall into the pit and be trapped.
Secret #2: There is a rainbow hiding inside the cake. The leprechaun will discover this as he eats his way to freedom.
You can see this effect in the image above from Omnomicon, the color poured in last is much more prominent than the color that went first, which is squeezed and spread around the bottom.
I really hoped to create a more traditional rainbow arch and distribute the colors so they would result in more even appearance so I decided to change the ratio of the colors of batter. The color poured first (in this case red) was given more batter than the color poured second (orange) and so on, the last color (purple) got the least amount of batter. I think it turned out fairly well. (But I see some room for improvement in the future.)
So this is what I did. I used one box of white cake mix and separated the batter into eight bowls:
- 6 ounces – red
- 5 ounces – orange
- 4 ounces – yellow
- 3 ounces – green
- 2 ounces – blue
- 1 ounce – purple
- 1 ounce – to be kept white
- the rest of the batter, also kept white
I used an angel food cake pan, but if you have a more rounded bundt pan I think it would work out even better as it would look more like a hill. update: I’m doing some tests in different pan shapes and finding that rounded pans and taller pans (or more cake batter put in an angle food cake pan) doesn’t create the same arch shape. I’m doing all sorts of test (yay for reasons to buy more cake pans) and I’ll report back when I find out more.
To make pouring the batter easier I filled plastic bags with each color then snipped the corner just before I needed it. I think this gave me a bit more control than scraping it from a bowl, but be aware that it’s difficult to stop the batter once it’s started so get a good hold on the bag before you start — one hand should be on top to squeeze the batter.
This makes for pretty dishes.
First pour the larger amount of white batter into the pan. Then pour the red batter in, making it a wide ring of batter. Then pour the orange over that, keeping it inside the red. I found it was easier to control the ribbon of batter holding the bag a bit higher over the pan and trying to be zen about it.
Pour in each color, creating narrower and narrower rings. As you go along snip smaller corners off the bags, it will help you control the narrower shape you are trying to make.
Last pour the remaining ounce of white batter on top. I had hoped this would make the rainbow dome have a more hollow center but mine didn’t quite turn out, so you might not even bother with this last one unless you’re feeling ambitious.
Put the cake in the oven, you might consider baking it at 325 instead of the usual 350 as it will dome a bit less when baked at a lower temperature. I forgot to do this.
While the cake is baking you can create your pretzel ladder. I used milk chocolate candy melts as glue, dabbing it in place using a toothpick then setting the smaller pretzels on top. I held the pretzel rods in place by supporting them with quarters. You might want to remember to wash your quarters first if you anticipate anybody eating the ladder. Ooops.
Here is the ladder in better light. (I bake at night, it doesn’t make for great photos. My deep apologizes for the assault on your eyeballs.)
Level off what will be the bottom of your cake, this will also help shape the base of the rainbow arch as the batter will curve under itself creating more of a rainbow horseshoe.
Flip it right side up onto your cake plate, then slide a few rectangles of parchment paper under the edges so you can be messy while frosting the cake. When you are ready to present it you simply pull the parchment paper away and, ta da, an effortlessly clean cake plate. I learned this on the old Martha Stewart show. I miss that show.
To frost the cake I made a half batch of the Magnolia Bakery buttercream frosting recipe found at MarthaStewart.com. First I did a crumb layer, followed by a few minutes in the freezer. (It’s amazing I can make room in my freezer for something like this.)
I used at Ateco 234 tip, it’s one of the larger ones. Probably not the best for creating something like grass but I already owned it so I went with it.
I sunk some pretzel sticks over the middle hole in the cake to create a sneaky platform for our gold.
Then I simply piled foil wrapped gold coins over the pretzel bars.
I created a sign using the international image for “Hey, the end of the rainbow and the pot of gold are over here!”.
And stuck the sign into the cake using a popsicle stick.
- You will stain your lips green while eating this.
- My cake plate tilts to one side.
- And I completely forgot to add the vanilla to the frosting.
- Bake at a slightly lower temperature, say 325, to avoid doming.
- If you use cake batter from scratch here is how I decided how much batter to separate out for colors — I took 2/3rds of the batter for color and divided that in amounts of 6/5/4/3/2/1 parts. In my cake the total batter was 34 ounces. Two-thirds of that is 22 ounces. Happily 6 + 5 + 4 + 3 + 2 + 1 = 21 ounces, which was close enough. YMMV (your math may vary).
Notes on different cake pan shapes:
- I baked rainbow cakes in a bunch of different shapes of cake pans and took photos of the results. Turns out? The rainbow arch effect works best in the angel food cake pan. Otherwise the colors swirl a bit more, still very pretty but more tie dye than rainbow.