Preheat oven to 350°F (177°C). Grease and lightly flour 4 9-inch round cake pans*, line with parchment paper rounds, then grease the parchment paper. Parchment paper helps the cakes seamlessly release from the pans. (If it’s helpful, see this parchment paper rounds for cakes video & post.)

Whisk the flour, baking powder, baking soda, and salt together in a large bowl. Set aside. Using a handheld or stand mixer fitted with a paddle attachment, beat the butter on high speed until smooth and creamy, about 1 minute. Add the sugar and beat on high speed for 5 full minutes until creamed together fairly well. Scrape down the sides and up the bottom of the bowl with a rubber spatula as needed. On medium-high speed, add 1 whole egg at a time, beating well after each addition until all 3 whole eggs are mixed in. Then, repeat with each egg yolk until all 4 egg yolks are mixed in. Beat in the vanilla extract. Scrape down the sides and up the bottom of the bowl with a rubber spatula as needed.

With the mixer on low speed, add the dry ingredients in three additions alternating with the buttermilk, beginning and ending with the dry ingredients, and mixing each addition just until incorporated. Do not overmix this batter. The batter will be smooth, velvety, and slightly thick. Spoon/pour batter evenly into each cake pan.

Bake for around 25 minutes or until the cakes are baked through. To test for doneness, insert a toothpick into the center of the cake. If it comes out clean, it is done. Allow cakes to cool completely in the pans set on a wire rack. The cakes must be completely cool before frosting and assembling.

Using a handheld or stand mixer fitted with a paddle attachment, beat the butter on high speed until pale, smooth, and creamy, about 2 minutes. Using a fine mesh strainer or sieve, sift the confectioners’ sugar and cocoa together. Add the sugar/cocoa mixture to the butter, then beat on low speed for 20 seconds. Stop the mixer, then add the milk, corn syrup, vanilla, and salt. Beat on medium-high speed for 2 minutes. If the frosting is too thick, beat in an extra splash of milk.

Grab a 3 and 1/2- to 4-inch circle cookie cutter (I use a large thin-edged cup) and cut a hole into two of the cake layers. Alternatively, you can cut a piece of parchment paper that size and use a sharp knife to trace/cut the holes. Place one of the whole cakes on a cake turntable, cake stand or serving plate. Use an offset spatula or knife to frost the top of the cake, then place one of the cut/holed cakes on top. Frost the top and inside the cavity. Place the other cut/holed cake on top and, once again, frost the top and inside the cavity. Fill the cavity with candies all the way up to the top. Place the last whole cake on top and frost the top and sides of the entire cake. Decorate with frosting and additional candies however you’d like. I used a Wilton 1M tip to pipe frosting around the top.

Slice, serve, enjoy! (Keep a spoon handy when serving. I like to pile additional candies that fall out of the center of the piñata cake onto each slice as I serve.)