I did it again! I have created another “hidden rainbow cake” and it’s got all the qualities of the hidden rainbow bundt cake, but it’s more party friendly and, most importantly for the kids (ok me), – is that it’s a great vehicle for LOTS of yummy buttercream! Btw, friends, today happens to be something called National Find A Rainbow Day. The absolute perfect day to debut these cuties.
Last summer someone had asked me if my rainbow bundt cake could be made into cupcakes and I decidedly responded no. If you tried building it into the muffin cup, you could get a swirl, or a horizontal line through, but you would not be able to get the arch shape, which really is the best part of that cake.
But I thought about it A LOT since then. Like, way more than any non-crazy person should be thinking about how to get a rainbow in a cupcake. And I came up with a combination of my rainbow cake method and the way surprise heart cupcakes are made…
So, first, we are going to make a small rainbow cake (like really tiny), slice it into perfect little rainbows, put them into muffin liners and surround the rainbows with white batter. On the outside they will look like plain vanilla cupcakes but slice them in half and OOOOO! Magic!
Steps to make Hidden Rainbow Cupcakes
Make the tendermost delicious white cake batter using the reverse creaming method; so, butter flour and sugar all creamed together in the first step. The eggs and liquids come after.
Remove part of the white batter (about 10 tablespoons, divided into 5 bowls with two tablespoons per bowl).
Color each bowl with your rainbow colors.
Layer the batter beginning with red, ending with purple. Add white batter on top.
Bake the rainbow! Once cool, slice into just under 1” tiny rainbows.
Ready a muffin tray with liners and a tiny bit of white batter to hold the rainbows in place.
Put rainbows in the center, fill the rest of the liner with white batter. Bake cupcakes!
Tips for Success
Take time to whip in your egg whites, one at a time, allowing a full minute to pass before you add another.
The baby rainbow can be a tricky one to build. I have messed it up SO many times (and still do!). The good news is that if your first rainbow doesn’t come out the way you like, you can make another with the same white batter. This will ultimately mean less cupcakes but more white batter can be made if necessary.
So that you know where to slice, add a little mark on your liners as an indicator for which way your rainbow is facing. This way you’ll get some clean cuts.
Notes on Surprise Rainbow Cupcakes
This is the ring mold you’ll need to make the tiny rainbows. If you plan on making a double batch, you’ll either need two of the pans or you’ll need to use it twice as each pan will give you about 12 little rainbows.
The white cake recipe is an adaptation of BraveTart’s white mountain cake. My flavorings are a tad different than hers but the main area where I depart from her recipe is in the method; I use a reverse creaming which produces a finer, tighter crumb, perfect for showcasing our internal design.
Find coconut oil at any grocery store, as it is not interchangeable with any other oil. Coconut oil is solid at room temperature, like butter, where other oils are not so please do not substitute! The coconut taste does not come through in the final cake; the result is a very childhood nostalgic flavor due to the two different types of vanilla.
For the buttercream I like to add… buttermilk! This is a non-traditional choice but I find that it adds creaminess and mellows out the overly sweet taste of a typical american buttercream. Feel free to add heavy cream or milk instead.
Hidden Rainbow Cupcakes
Wrapped up in the most nostalgic of white cake flavors, is a cupcake with a hidden, magical surprise.
113g or 1/2cupbutterunsalted and at room temperature
60g or 1/3cupcoconut oilrefined
210g or 1cupgranulated sugar
1/2teaspoonfine sea salt
4large egg whites
2teaspoonspure vanilla extract
240g or 1cupbuttermilk
Double Vanilla Buttercream
226g or 1cupunsalted butterat room temperature
2teaspoonspure vanilla extract
1/2teaspoonfine sea salt
400g or 3cupsorganic powdered sugarsifted
1-2tablespoonsmilkbuttermilk, or heavy cream
Make the batter:
In the bowl of a stand mixer beat together the butter, sugar, cake flour, coconut oil, vanillas, salt, baking powder and baking soda.The mixture should be sandy looking, all the oils coating the flour.
Add the egg whites, one at a time, beating between each addition. Scrape down the bowl as needed.
Turn the mixer to low and pour in the buttermilk while it’s running. Turn speed to medium and let beat until well mixed, shouldn't take more than a minute.
Make the small rainbow bundt:
Butter and flour the small ring mold.
Into five small bowls add 2 tablespoons batter. Color each bowl to your liking. For the red I like to add another tablespoon of batter because it is the base.
In the 5” ring mold, spread the top color of your rainbow (so, red) around the bottom of the mold - try to get it to go up the sides a bit to get a better arch. Then spread the orange but leave a little bit of red border on either side. Follow with each color, the width of the circle should get smaller and smaller, so you can see each color on the side at the end with the purple. After the purple do a ring of plain white batter in the center of the purple.
Bake the small cake for 12-15 minutes at 350. When it is done, allow it to cool for a few minutes in the pan then invert it onto a cooling rack. To speed up the cooling period, place it in the freezer. You don’t want to slice it while it is warm otherwise you won’t get clean cuts. Once it is completely cool and firm, cut it into 1/2 inch slices.
Make the cupcakes:
Line a 12 cup muffin pan with paper liners. Into the bottom of each cup, smear just a bit of batter, about a half tablespoon. Place your little rainbows in the center of the cups. I do this so they are all facing the same direction, that way when I want to slice them to reveal the rainbow, I know which way to cut. You can also make little markers in the cupcake liners to guide you.
Over the little cake rainbow, pour white batter. Get the batter all around and above the rainbow. The cups should be about 2/3 full.
Bake the cupcakes for about 20 minutes, check for doneness by pressing the top gently to see if it feels dry. You might see some of the arch peeking out at the top of the cupcake, it's ok! Let cool completely.
Make the buttercream:
In the bowl of a stand mixer, beat the butter with the vanillas and salt for about 5 minutes, until the butter is light and fluffy. Add the powdered sugar and beat until combined, about 3 minutes. Add the buttermilk and beat to just combine.
Pipe or spread the buttercream.
To slice in half to reveal the rainbow, first chill the cupcakes fully - either in the fridge for 30 minutes or 10 minutes in the freezer. Use your marker to guide the knife to slice in half.
Makes: 12 cupcakes. Takes: 2 hours, plus cooling time