Make the icing first: The icing needs to completely cool and thicken, so prepare it first. Combine the butter, chocolate, granulated sugar, heavy cream, and corn syrup together in a medium saucepan over medium heat. Stir constantly until butter has melted. Once melted, stir occasionally as the sugar dissolves and the mixture comes to a boil. Allow to boil for 1 minute. Remove from heat and stir in the vanilla extract. Taste (it’s warm, so be careful!) Add a sprinkle of salt, if desired. I always add a pinch. Leave uncovered and set aside to thicken and cool for at least 1-2 hours or until it has a spreadable consistency. This is enough time to bake and cool the cake layers.

Preheat oven to 350°F (177°C). Grease three 9-inch cake pans, line with parchment paper rounds, then grease the parchment paper.

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 or whisk attachment, beat the butter and sugar together on high speed until smooth and creamy, about 3 minutes. Scrape down the sides and up the bottom of the bowl with a rubber spatula as needed.

On medium-high speed, add 1 egg at a time, beating well after each addition. Beat in the vanilla extract.

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.

Pour slightly less than 1 cup of batter into prepared cake pans. Bake for 12 minutes or until a toothpick inserted comes out clean. Allow to cool for a couple minutes, then carefully invert the cake onto the counter. Peel off the parchment to reuse.

Carefully place one layer on a serving platter, cake turntable, or cake stand. Spoon and spread ¼ cup of icing on top, then repeat with the rest of the cake layers and icing. Some icing will spill over the sides and that’s ok! Decorate the top with sprinkles, if desired.

Set cake aside for at least 30 minutes before slicing and serving. Cover and store leftover cake at room temperature for 1-2 days or in the refrigerator for up to 1 week.