• Place the crumbled cake and buttercream frosting into a medium sized bowl and combine them with a rubber spatula until the mixture sticks together. It should be tacky enough to form balls when you roll it between your hands. If it's not quite that tacky yet, add more buttercream a Tablespoon at a time until it reaches the proper consistency.
• Use a Tablespoon to scoop the cake/buttercream mixture and then roll it between your hands to form a 1 inch ball. Place it on a lined baking sheet and continue forming balls until you have used all of the cake/buttercream mixture.
• Pour the rainbow sprinkles (or topping of your choice) onto a small plate or into a small bowl. Roll each ball through the sprinkles until the surface is covered and place back onto the lined baking sheet. Refrigerate the sprinkle cake truffles for at least 20 minutes, after which they should be firm and ready to place on your cake (or enjoy as-is!)

Make the Yellow Cupcakes

• Preheat the oven to 350ºF/177ºC and line a cupcake pan with 12-15 liners.
• Add the sifted cake flour, baking powder, baking soda, and salt into a bowl and whisk to combine. Set aside. 
• In the bowl of your stand mixer (a handheld mixer works fine too!), cream the butter for on high for two minutes until it's light and fluffy. Add vegetable oil and sugar, then continue to mix on med-high for another two minutes. Add the whole egg and egg yolk and mix until well combined. Add vanilla and sour cream and mix for one minute on high, scraping down the bowl and paddle once more. 
• With the mixer on low speed, add in the dry ingredients and mix until just combined, then continue mixing while you add the milk in a slow stream. Mix until just incorporated, then scrape down the sides and bottom of the bowl and give it a few stirs to make sure there are no lumps (without over-mixing). The batter will be thick.
• Spoon the yellow cake batter into the cupcake liners, filling each one between 1/2 and 2/3 full. Bake for 15-18 minutes, or until a toothpick inserted comes out clean. Allow the cupcakes to cool fully before frosting.

Make the Chocolate Buttercream

• In a stand mixer fitted with a paddle attachment, whip the butter on high speed until creamy and light in color, about five minutes. Scrape down the bowl and paddle and turn the mixer to low, then add the powdered sugar, cocoa powder, milk, vanilla extract, and salt. Continue mixing on low speed until fully combined and uniform, 2-3 minutes, scraping down the bowl and paddle as needed.

Assembly

• When the cupcakes are fully cooled, fit a piping bag with Wilton Tip 1M. Fill the piping bag with the chocolate buttercream and pipe a swirl onto each cupcake. Garnish with rainbow sprinkles.

Make the Yellow Cake

• Preheat the oven to 350°F. Prepare three 6-inch cake pans or two 9-inch cake pans by spraying the sides with a cooking spray (Baker's Joy is my favorite) and a wax paper circle fitted to the bottom of the pan. Alternatively, you can grease and lightly flour the pans. 
• Sift the cake flour and then measure by spooning and leveling it in your measuring cup. Add the cake flour, baking powder, baking soda, and salt into a bowl and whisk to combine. Set aside. 
• In the bowl of your stand mixer (a handheld mixer works fine too!), cream the butter for on high for two minutes until it's light and fluffy. Add vegetable oil and sugar, then continue to mix on med-high for another two minutes. Add the whole eggs and egg yolk one at a time, mixing thoroughly after each addition. Add vanilla and sour cream and mix for one minute on high, scraping down the bowl and paddle once more. 
• With the mixer on low speed, add in the dry ingredients and mix until just combined. Add the milk slowly and mix until just incorporated. Scrape down the sides and bottom of the bowl and give it a few stirs to make sure there are no lumps (without over-mixing). The batter will be slightly thick, but pourable.
• Pour batter evenly into prepared cake pans (no more than 2/3 of the way full) and bake for 30-35 minutes. They're done when they spring back to the touch and a toothpick inserted into the middle comes out clean. Let the cakes cool in the pan for five minutes before turning them out onto a wire rack for an additional few hours of cooling. Make sure they're entirely room temperature before applying any frosting. 

Make the Chocolate Buttercream

• In a stand mixer fitted with a paddle attachment, whip butter on medium speed until creamy and light in color, about four minutes. Scrape down the bowl and paddle and turn the mixer to low, then add powdered sugar, cocoa powder, milk, salt, and vanilla extract. Increase the speed to medium and beat for two full minutes.

Assembly

• Once the cakes have cooled, torte them before filling and frosting with chocolate buttercream. To create the design pictured, use an icing scraper to smooth the sides and make them straight, then gently drag a cake comb through the buttercream to create lined texture. Use Wilton Tip 1M to create a rope border around the top edge by piping overlapping rosettes. Add rainbow sprinkles to finish the look!

Make The Banana Cupcakes

• Preheat the oven to 350ºF and prepare a muffin pan by lining with cupcake tins. Measure the flour by spooning into your measuring cup and leveling it, then whisk it together with the baking powder, baking soda, salt, and ground cinnamon and set aside.
• Place the bananas in the bowl of your stand mixer and mash them with a paddle attachment on medium for about 30 seconds. Set aside.
• Cream the butter on high for 1 minute. Add the white and brown sugars and cream on high for another 2 minutes. Turn the mixer to low, add the eggs one at a time and mix until combined.  Add the mashed bananas and vanilla and beat for 1 full minute, then scrape down the bowl and paddle. With the mixer still on low, add the dry ingredients until just combined, then add the buttermilk and mix until just combined. Give it a few stirs with your spatula to ensure that everything is nice and mixed up without overmixing. The batter will be thick.
• Spoon the batter into prepared cupcake tins ⅔ of the way full, then bake for 17 minutes, or until a toothpick inserted comes out clean. Cool the cupcakes in the pan for five minutes before removing and continuing to cool on a wire rack or flat surface.

Make The Vanilla Buttercream

• With a hand mixer or paddle attachment on your stand mixer, cream the butter on medium-high until it’s creamy and light (almost white) in color. About 7 minutes. 
• Add the sifted powdered sugar, one cup at a time, scraping down after each addition and making sure each cup is fully incorporated before adding the next one. Add vanilla, milk, and salt and mix on medium-low for another two minutes until fully incorporated. 
• Place the buttercream into an airtight container and chill in the refrigerator until ready to use.

Make The Chocolate Ganache

• Place chocolate chips into a heat resistant bowl (glass or metal). In a saucepan over medium-high heat, warm heavy whipping cream until it just starts to boil. I always look for small bubbles forming around the edge and a soft boil starting in the middle. When you see that it’s just starting to boil, pour it into your bowl of chocolate and let sit for 30 seconds, then whisk it together until it's uniform in consistency and there are no bits of chocolate left on your whisk.
• Cool ganache at room temperature for about 30 minutes, or until the ganache itself is room temperature. 

Assembly

• Once the Banana Cupcakes have cooled completely, add a scoop of cold Vanilla Buttercream on top of each one and shape it with a spoon until it resembles a scoop of real ice cream. Drizzle the buttercream with Chocolate Ganache (make sure it's room temperature, not hotter or colder than that), add the rainbow sprinkles, and place a maraschino cherry on top.