FOR THE CAKE
Cooking spray
2 c. all-purpose flour
3 tbsp. cornstarch
1 1/2 tsp. baking powder
1 tsp. kosher salt
1 c. (2 sticks) butter, softened
1 c. granulated sugar
1/2 c. packed brown sugar
2 large eggs, plus 6 egg yolks
2 tsp. pure vanilla extract
3/4 c. milk
FOR THE FROSTING
1 c. (2 sticks) melted butter
3 c. powdered sugar
1 c. unsweetened cocoa powder
1/3 c. heavy cream
1 tsp. pure vanilla extract
Pinch of kosher salt
Step 1
Make cake: Preheat oven to 350°. Line two 8" round cake pans with parchment paper and grease with cooking spray.
Step 2
In a large bowl, whisk together flour, cornstarch, baking powder, and salt. In another large bowl using a hand mixer (or in the bowl of a stand mixer fitted with the paddle attachment), beat together butter and sugars until light and fluffy. Add eggs and yolks, one at a time until well combined, scraping down sides of bowl occasionally, then add vanilla.
Step 3
Add dry ingredients to wet ingredients and mix until just combined, then add milk and mix until combined.
Step 4
Divide batter evenly between prepared pans and bake until a toothpick inserted in the middle comes out clean, 25 to 30 minutes. Let cool 10 minutes, then invert onto a wire cooling rack to cool completely.
Step 5
Meanwhile, make frosting: In a large bowl, beat together melted butter, powdered sugar, and cocoa powder until smooth. Add cream, vanilla, and a pinch of salt and beat until light and fluffy.
Step 6
Level cakes with a large serrated knife by holding knife horizontal to cake and slicing a thin layer off the tops until even. Add about half of icing to one layer of cake and spread into an even layer. Top with second cake layer and frost with remaining icing.