This Rainbow Cake, complete with a marshmallow frosting and Lucky Charms cereal, is the perfect show-stopper for your upcoming St. Patrick’s Day celebration! Inspired by gold coins, rainbows, and, of course, the luck of the Irish, this rainbow cake is the best way to get you in the mood for St. Patty’s Day!
St. Patrick’s Day Celebration
Planning a Saint Patrick’s Day Party?! BFFF has YOU covered with this rainbow party cake! This would be such a fun addition to your upcoming celebration, incorporating flecks of gold, pastels and all things Lucky Charms! I am seriously over the rainbow with this cake from our talented contributor Ashley Byma. But just in case you’re feeling like this isn’t totally obtainable, it’s okay! While I know this design may seem daunting to many (yes, including me), this is a great opportunity to screenshot these pictures as inspiration! If you’re not quite up to baking this rainbow cake recipe, take the idea to your favorite local bakery and have them duplicate it. Gather your best friends to come over and share a slice and get into the St. Patrick’s Day spirit!
Best White Cake Recipe
This fun Saint Patrick’s Day cake starts out with one package of white cake mix – thank goodness! Raise your hand if you use cake mixes from time to time like me?! Seriously, some days the semi-homemade route can be a total life-saver. I just love how easy this batter is to put together as you doctor up the cake mix. To get things going, preheat your oven to 350 degrees, and prep three 6-inch cake pans with cooking spray, also lining the bottoms with parchment paper so your cake doesn’t stick! Add your cake mix into your bowl, then add ground lucky charms cereal (without the marshmallows, because we’ll use those later!), sugar and salt. Once your dry ingredients are combined, switch to the paddle attachment and mix in sour cream, vegetable oil, vanilla extract, and three eggs. My favorite part of this recipe is the addition of the Lucky Charms milk, which should be prepped 45 minutes before you start mixing your batter to really get that Lucky Charms flavor.
How To Bake A Cake
Once your batter is ready, you can add food coloring to it if you’d like. Then, separate the batter evenly into your three cake pans and bake them for 25 minutes. Once you test your cakes with a toothpick to make sure they’re fully baked, set them aside to cool. Once your cakes are cool, wrap them in saran wrap and place them in the freezer to avoid crumbling for when it’s time to decorate this fun rainbow cake!
Perfect Marshmallow Frosting
While your cake is baking, prepare your marshmallow frosting! Yes, you absolutely read that right – this cake is filled with layer upon layer of creamy, fluffy marshmallow frosting. And yes, it’s so good you could definitely eat it by the spoonful! ;) To make the frosting, add butter and marshmallow crème to your stand mixer and beat until light and fluffy. Add in the powdered sugar one cup at a time, taste-tasting as you go to be sure your frosting doesn’t end up too sweet. Add in vanilla extract, a pinch of salt and heavy whipping cream, and then mix until it’s well combined and totally smooth.
Swiss Meringue Buttercream Recipe
Swiss Meringue Buttercream is definitely an all-time favorite for cake bakers because of how smooth it is. All of those picture-perfect cakes you seen on Pinterest with the incredibly smooth frosting usually use Swiss Meringue. It’s incredibly light and fluffy, making it not only super useful for decorating cakes, but incredibly delicious! To make this buttercream, you’ll need sugar, egg whites, salt, butter, and vanilla extract. Whisk your sugar, egg whites, and salt together until combined, while you heat a small amount of water in a saucepan until boiling. Create a double boiler with your mixing bowl and saucepan, whisking continuously while the egg mixture heats up. Begin mixing in a stand mixer, starting on low and gradually moving to high, until the meringue is glossy with stiff peaks. Lastly, mix in your butter until smooth, then add in the vanilla extract, switching out the whisk for the paddle attachment to beat the frosting on medium until smooth.
How to Frost a Cake
Once it’s time to start assembling this Lucky Charms inspired cake, it takes a few steps, but the end result is so worth it. Be sure you start with flat cake layers. Just in case the cake layers didn’t bake evenly, use a bread knife to trim off the top before you get started. Start with your first frozen layer on a cake board. Pipe a circle of buttercream around the border of the cake to create a barrier before spreading the marshmallow frosting over top. Cover the frosting with a layer of Lucky Charms cereal – marshmallows included! Repeat this step with the remaining cake layers, and then frost the outside with the remaining Swiss Meringue Buttercream.
Rainbow Party Cake
For all of you putting together a St. Patrick’s Day celebration, or, simply planning to spread joy with your friends and family around the holiday, add this cake to your list. It’s a great inspiration for Saint Patrick’s Day and the perfect pastel kick-off to spring! And remember, if you’re not an expert baker, it’s totally okay. This recipe offers some great short-cuts to offer a more semi-homemade approach, or simply use it as inspiration with your favorite cake decorator. I’d love to hear what you end up doing with this fun recipe. Sending you all four-leaf clovers and pots of gold! Be sure to let me know in the comments how you celebrate Saint Patrick’s Day!
Rainbow Party Cake
Lucky Charms Cake:
- 1 package white cake mix
- 1 cup Lucky Charms flour finely ground cereal without marshmallows
- 1 cup granulated sugar
- ¾ teaspoon salt
- 1 cup sour cream
- 2 tablespoons vegetable oil
- 2 teaspoons vanilla extract
- 3 eggs
- 1 cup Lucky Charms cereal milk* 2 cups cereal + 1 cup whole milk
- 1 stick unsalted butter slightly cold
- 1 7 oz jar marshmallow crème
- 1-2 cups powdered sugar
- 1 teaspoon vanilla
- Pinch salt
- 1 tablespoon heavy whipping cream
- 1 batch of SMBC recipe and directions found here
- Add Lucky Charms and milk to a large bowl and let sit for about 45 minutes – 1 hour.
- Reserve the milk and set aside.
Lucky Charms Cake:
- Preheat oven to 325° F. Spray three 6-inch cake pans with cooking spray, and line the bottoms with parchment paper.
- In the bowl of a stand mixer fitted with a whisk attachment, add the dry cake mix, ground Lucky Charms, sugar, and salt. Mix until combined.
- Switch to the paddle attachment and add sour cream, vegetable oil, vanilla, eggs, and cereal milk. Mix on low-medium speed just until combined but do not overmix. You can add any food dye at this time if you wish (I used turquoise).
- Pour 1/3 of the batter into each cake pan and bake for about 25 minutes or until the middle is set. Insert a toothpick in the middle of the cake to test. You may have leftover batter (yay cupcakes!)
- Remove from oven and let cool. Transfer to countertop covered with parchment paper by running a knife around the cake edges, then turning the cake pan upside down to release the cake. Once completely cool, you can wrap these in saran wrap and place in a gallon size freezer bag; you can freeze the cake layers for about 2 months. When ready to fill the cake, use frozen cake layers to prevent the cake from crumbling while decorating.
- Add butter and marshmallow crème to the bowl of a stand mixer fitted with a paddle attachment. Beat on medium speed until light and fluffy.
- With the mixer on the lowest setting, slowly add powdered sugar, one cup at a time. This is a very sweet frosting so you will want to taste test before adding all of the sugar.
- Add vanilla, salt & heavy whipping cream and mix on medium speed until combined and smooth.
- If the cake layers do not bake evenly, you can use a bread knife to trim the top off and make it flat which is easier for decorating. If you froze the cake layers, you will need to let the cake layers thaw just a bit before trimming.
- Start with the frozen/semi-thawed cake layers, and place one layer on a cake board. You can use a spoonful of buttercream as “glue” between the cake layer and cake board if you like.
- Pipe a circle of buttercream around the perimeter of the cake layer to create a barrier before adding the marshmallow frosting (this will prevent the marshmallow from spilling over the edges of the cake). Spread an even layer of buttercream over the top of the 1st cake layer.
- Cover the marshmallow frosting with a layer of Lucky Charms cereal (including marshmallows!)
- Repeat with remaining cake layers and frost the outside with the swiss meringue buttercream.
- If you choose to put cereal between the cake layers, it’s best to keep the cake refrigerated & eat the cake within a day or two so the cereal doesn’t get soggy.