01 -
Preheat oven to 175°C. Grease and flour three 15cm round cake pans.
02 -
In a bowl, whisk together the all-purpose flour, cornstarch, baking powder, and salt. Set aside.
03 -
In a stand mixer, cream unsalted butter with granulated sugar until pale and fluffy. Add vegetable oil and vanilla extract, and mix until smooth.
04 -
Add eggs one at a time, beating well after each addition. Follow with the egg yolks, ensuring batter remains smooth.
05 -
With the mixer on low speed, alternately add portions of the flour mixture and buttermilk to the creamed mixture, beginning and ending with the dry ingredients. Mix just until incorporated.
06 -
Divide batter evenly among prepared pans. Bake on the center rack for approximately 30 minutes, or until a skewer inserted in the center emerges clean.
07 -
Allow cakes to cool in pans for 10 minutes. Turn out onto a wire rack and cool completely before frosting.
08 -
Melt 56g butter and mix with cocoa powder in a small bowl. In a separate bowl, melt semisweet chocolate with 30ml of milk until smooth. Beat 227g room-temperature butter in a mixer until creamy, then add the cocoa butter mixture, powdered sugar, remaining milk, and melted chocolate mixture. Beat until light and fluffy.
09 -
Once cakes are completely cool, spread or pipe chocolate frosting between layers. Cover top and sides with remaining frosting for a smooth finish.