Funfetti Cake. Preheat the oven to 350F. Prepare 5 8-inch cake pans by greasing the sides with room-temperature butter, and a wax paper circle fitted to the bottom of the pan. Or, you can grease and lightly flour the pans.
Sift the cake flour, and add the cake flour, baking powder, baking soda, and salt into a bowl and whisk to combine. Set aside.
In a stand mixer bowl, cream the butter for on high for two minutes until light and fluffy.
Add in the sugar and continue to mix on medium-high for two minutes, scraping down the sides of the bowl and the paddle as needed.
Add in the eggs, one at a time, mixing thoroughly after each addition.
Add vanilla and the sour cream, and mix for one minute on high speed, scraping down the sides of the bowl as needed.
With the mixer on low speed, add in the dry ingredients, and alternating mixing with the milk, and mix until just combined, scraping down the sides of the bowl. If there are lumps in the batter, stir the mixture until they are gone.
In a small bowl, coat the rainbow sprinkles with 1 ½ tbsp. of all-purpose flour. Gently fold in the rainbow sprinkles into the batter by hand. The batter will be thick, but pourable.
Using a kitchen scale, measure out the total amount of batter. Divide the total weight by five, and measure out equal amounts of batter into 5 cake pans using the kitchen scale.
Bake for 35-40 minutes. Check to see if they’re done by inserting a toothpick into the center, and checking to see if it comes out clean with no batter on it.
Let the cakes cool in the pan for 5 minutes, then turn them out onto a wire rack for additional cooling. When room temperature, you may apply icing to the cakes and layer them.
Italian Buttercream Icing
Place the egg whites and ⅓ of the sugar a stand mixer bowl, and beat with a whisk attachment at medium-high speed, until the egg whites form soft peaks.
Meanwhile, pour the remaining sugar and ⅓ cup water in a medium saucepan over medium heat. Using a candy thermometer and not stirring, heat until 240F.
Continue to whip the egg whites on medium-high speed, and slowly drizzle in the hot syrup, in between the side of the bowl and the beaters. Continue to whip until both the bottom of the bowl and the mixture are cool, or about 10 to 15 minutes.
When the mixture is thick and forming peaks, beat in the salt.
While still beating, add the butter a few pieces at a time. As the butter is added, the buttercream will thin out until all of the butter is added.
Beat in the vanilla extract. If the buttercream is still too loose, beat on high speed.
Use right away, or refrigerate in an airtight container.
Buttercream Icing
Beat the butter at high speed until creamy, around 5 minutes, scraping the sides of the bowl.
Gradually add sugar and milk alternatively, while beating at a low speed.
Add in vanilla extract, then beat for 8 - 10 minutes on high speed, scraping the sides of the bowl into the mixture.
Lollipops
Place 3 large silicone mats onto a flat surface.
Place the fondant decorations face down on the silicone mats, with enough space to form full lollipops.
Pour the sugar, water, and corn syrup in a medium saucepan over medium heat.
Gently stir until the mixture comes to a boil, making sure to not splash the mixture around the sides of the bowl.
Once boiling, stop stirring (and do not stir for the rest of the cooking) and use a silicone brush moistened with warm water to wipe down the sides of the saucepan, to wash away any crystals forming.
With a candy thermometer, check the temperature of the mixture. When at 300F, take the saucepan and put the bottom into a tub of room-temperature water for 30 seconds.
Mix in the flavor extracts and colorings that you want into the saucepan.
Pour out the mixture onto the cookie sheet on top of the fondant decorations.
Lay the lollipop sticks in the center of the lollipop, and spin the stick so it is completely surrounded by candy.
Repeat with remaining candy, doing 3 at a time.
Let harden for 20 minutes.
Cake assembly
Take the cakes out of the freezer, but do not defrost them.
Using a lazy susan or cake decorating turntable, and place a cake base on top. Apply a little buttercream to the cake base, and take a single layer of cake and ice the top with the traditional buttercream. Place another layer on top, and repeat until you have a full 5-layered cake.
With the lazy susan, ice the entirety of the outside with the italian buttercream using an icing smoother.
Soon after icing, apply the fondant snowflakes to the cake.
Set the near-finished cake into a plastic container to unfreeze the night before serving, or for 10 hours to completely defrost.
When defrosted, stick the lollipops into the top of the cake.