Prepare the cake layers by lightly oiling the insides of three 6” cake pans. Place a parchment round in the bottom of each pan (see note) and rub oil on it. Preheat the oven to 350°F
Combine the butter and sugar in the bowl of a stand mixer fitted with the paddle attachment. Beat on medium-high speed for 3-5 minutes, or until it is fluffy and light in color.
Stop the mixer, scrape down the sides and then put the mixer on a low speed. Incorporate the egg whites one at a time until completely combined, scraping down the sides as needed. Add in the extracts until just combined.
Whisk together the flour, baking powder and salt in a bowl. Add half of the flour to the butter mixture and stir until combined. Add in the milk until completely integrated, then finish with the last of the flour.
Separate the batter evenly into three containers. Add some green food coloring into the first container, a little more to the second and twice as much into the last. Stir until blended completely and pour into prepared cake pans.
Bake in the preheated oven until a toothpick inserted in the center comes out clean, about 25 minutes. Allow the cake layers to cool in the pan until the edges start to separate from the sides of the pan. This takes about 10 minutes Turn out onto wire racks to cool completely before frosting.
Irish Cream Frosting
Beat the butter with a paddle attachment on high speed until creamy and fluffy, about three minutes. Scrape down the sides, add the salt and powdered sugar and beat on medium for another two minutes. Reduce the speed to low and add in the marshmallow fluff and Irish Cream. If the consistency is not spreadable, add one tablespoon of Irish Cream at a time until the frosting has thinned out.
Separate the marshmallows from the cereal, placing them in individual containers based on shape.
Separate the frosting into fourths. Place one cake layer on a cake plate or stand and evenly spread one of the frostings onto the layer. Don't be nervous if it starts spilling over the side. Repeat the process with the rest of the layers, reserve one frosting for later.
Using a spatula or bench scraper, scrape the excess frosting from the top and sides of the cake. Make the crumb coat very thin. Smooth the edges of the top layer as needed to make them flush with the top. Place it in the refrigerator to chill for 30 minutes (or freezer for 10).
Remove the cake and spread the remaining frosting around the outside of the cake. Use a spatula or bench scraper to make it smooth.
Following the pattern of the jingle, place the marshmallows in a single row all the way around the cake (see note). Start the next layer one marshmallow over from where you began previously (heart on top of stars). Repeat this process until the entire cake is covered.
Sprinkle some of the crushed cereal from the bottom of the bag on top of the cake for texture. Cut, and serve.
If you don't have parchment rounds, you can make one yourself by tracing the bottom of the pan onto parchment paper, then cutting it out.You can use any order you like for the marshmallows, but if you choose to follow the jingle the order is: heart, stars, horseshoes, clovers, blue moons, unicorns, rainbows, and red balloons.