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Funfetti Rice Krispies Treat Cake

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This Rice Krispie Treat Cake tastes JUST like rice krispie treats! With rice krispie cereal in the cake batter and the buttercream, and lots of sprinkles all around, this cake is a perfect way to bring a plate of cheer to any celebration!

Ingredients

Funfetti Rice Krispie Cake Batter

  • 1 cup buttermilk room temperature
  • 2 cups rice krispies cereal, divided 1 cup will be used for the cereal soak, and the other cup will be pulsed into a powder for the cake batter
  • 4 egg whites room temperature
  • 2/3 cup sour cream room temperature
  • 1/3 cup vegetable oil
  • 1 Tablespoon vanilla
  • 1/4 cup rainbow jimmies
  • 1 15.25oz Box White Cake Mix I prefer the taste and texture of Duncan Hines, but any other brand should be mostly similar

Rice Krispie Treat Buttercream

  • 1 1/2 cup (or three sticks) unsalted butter left out at room temperature for 10 minutes to slightly soften.
  • 3 cups rice krispies cereal, pulsed to a powder (after pulsing the whole cereal, you should have about 3/4 cup powdered cereal to add to the buttercream)
  • 1 cup marshmallow fluff
  • 1 pinch salt
  • 1 Tablespoon vanilla
  • 1/4 cup heavy cream, plus more if needed to thin out the buttercream
  • 7-8 cups powdered sugar

Rice Krispies Treats (optional for decorating)

  • 4 Tablespoons unsalted butter
  • 4 cups small marshmallows
  • 6 cups rice krispies cereal
  • 1/2 cup rainbow jimmies

Garnishes

  • 1/2 cup rice krispies cereal
  • 1/2 cup rainbow jimmies

Instructions

For the Funfetti Rice Krispie Cake Batter

  • In a small bowl, stir together 1 cup of the rice krispie cereal with the buttermilk and let soak for about 15-20 minutes. This will infuse the buttermilk with the cereal flavor. The longer it soaks, the more flavor it will have.
  • Preheat the oven to 325 degrees convection bake. (If using traditional bake, you'll just need to keep the cakes in the oven a couple minutes longer. Prep three 6" cake rounds, or two 8"/9" cake rounds with a swipe of shortening or dust of flour. Set aside.
  • In a large bowl, whisk together the cereal-soaked-buttermilk (don't strain the soggy cereal - just toss it all in there!), powdered rice krispie cereal, egg whites, sour cream, vegetable oil, and vanilla. Toss in the rainbow sprinkles and sift in the cake mix. Split the batter evenly between the prepared cake rounds. Bake for 25-27 minutes until the centers are baked through. Flip the cakes out onto a wire rack, and then let the cakes cool completely. Wrap them up in plastic wrap, then store them overnight fin the freezer for easy cake assembly.

For the Rice Krispie Treat Buttercream

  • In a bowl of a stand mixer fitted with a paddle attachment, whip up the butter until it's light and fluffy. Add in the cereal powder, marshmallow fluff, vanilla, salt, and heavy cream. Increase the speed until everything is combined. Scrape down the sides of the bowl with a spatula. Slowly add in the powdered sugar 1/2 cup at a time. Add a little more heavy cream (1 Tablespoon at a time) if needed. Flip the mixer onto a high speed until the buttercream has lightened in texture and is smooth and creamy.

For the Funfetti Rice Krispie Garnishes

  • Prep a 9x13 glass dish with either plastic wrap or cooking spray. Set aside. In a large pot over medium heat, melt the butter, then add in the marshmallows and stir. When the marshmallows have melted, add in the cereal and stir. Gently stir in the rainbow jimmies, press the krispie treats into the prepared 9x13 dish, and then let cool. Slice with a knife when you're ready to add them to your cake. There will be leftovers, so be prepared for a little snacking!

Assembly

  • Using a cake turntable and cardboard cake rounds, add on a dot of buttercream in the middle of the round. Spread the buttercream flat with an offset icing spatula, then place down the first cake round. Add on a layer of rice krispies buttercream, then add on the next cake round; making sure to line it up straight. Repeat with the final cake round. Crumb coat the cake, then freeze.
  • Add on the final layer of buttercream using a straight icing spatula and then a cake scraper for clean sides and edges. Place the cake onto a cookie sheet, then back onto the cake turntable. Add on a few sprinkles and rice krispie cereal pieces in random places around the outside of the cake.
  • Using a Wilton 6B or 8B piping tip, pipe a few dollops of buttercream around the top outside rim of the cake, then place a small cube of rice krispies on top to finish.
  • Enjoy!