Preheat the oven to 350 degrees and spray the 3 cake pans with baking spray.

Combine all cake ingredients into a standing mixer or large mixing bowl and beat until combined.

Divide the batter between the 3 pans and bake in the oven for 28-32 minutes or until a toothpick comes out clean.

Allow to cool completely before moving onto the cake board.

Using a cake leveler, remove the dome from the cakes to make even.

Using a standing mixer, beat together the butter, powdered sugar, vanilla, and heavy whipping cream until combined, smooth and stiff with peaks.

Scoop 1/2 cup of frosting into 4 bowls and mix in a few drops of food coloring into each bowl.

Using 1 cake layer on the cake board, scoop 1 cup of frosting onto the top of the cake and spread evenly.

Sprinkle ¾ cup of Lucky Charms cereal all over the frosting layer.

Place the second layer of cake on top of the first layer of cereal frosting and scoop another 1 cup of frosting onto the second layer of cake, spreading evenly.

Sprinkle another ¾ cup of Lucky Charms.

Place the last layer of cake on top.

Scoop ¼ cup of each colored frosting into their own bags and set aside.

Using a knife, blot dollops of the colored frosting all over the side of the cake.

Take a flat spatula and lightly spread the colored frosting to create a rainbow effect.

Pick out the marshmallows from the cereal and place them randomly on the sides of the cake.

Using the colored frosting, pipe dollops of frosting on top.

Fill the center top of the cake with Lucky Charms cereal.

Cut and enjoy!