Ingredients
Unsalted butter, room temperature
1 1/2 cups cake flour (not self-rising)
1 cup sugar, divided
1 1/2 teaspoons baking powder
1/2 teaspoon kosher salt
1/3 cup safflower oil
5 egg yolks plus 6 egg whites
1/2 cup whole milk
1 vanilla bean, split and seeds scraped
1/4 teaspoon cream of tartar
Caramel Buttercream Frosting
1 1/4 cups chopped malted milk balls, plus more for decorating (optional)
Caramel dots (see Cook's Note, below) and chocolate curls, for decorating (optional)
Preparation
Preheat oven to 325 degrees. Butter two 8-inch round cake pans. Line with parchment; butter parchment. In a medium bowl, whisk together flour, 1/2 cup sugar, baking powder, and salt. In a separate bowl, whisk together oil, egg yolks, milk, and vanilla seeds. Whisk egg-yolk mixture into flour mixture.
In the bowl of an electric mixer fitted with the whisk attachment, beat egg whites on high speed until frothy. Add cream of tartar and beat until soft peaks form. Gradually add remaining 1/2 cup sugar, beating until stiff, glossy peaks form, about 5 minutes. Whisk one-third of egg-white mixture into batter. Gently but thoroughly fold in remaining egg-white mixture with a rubber spatula. Transfer batter to prepared pans. Bake until tops spring back when lightly touched, about 25 to 30 minutes. Run a knife around edges of pans. Invert cakes onto a wire rack; remove parchment. Let cool completely, upside-down.
Using a serrated knife, split each cake horizontally into three equal layers. Place a cake layer on a cake stand or turn table. Spread 3/4 cup buttercream evenly over it, then sprinkle with 1/4 cup malted milk balls. Repeat with remaining 5 cake layers. Spread remaining buttercream over top and sides of cake. Decorate with more malted milk balls, caramel dots, and chocolate curls, if desired.
