Preheat oven to 180°C (350°F) conventional and grease and/or line two 8 inch cake tins.

In a bowl, sift together flour, cornstarch, baking soda, baking powder and salt. Using a whisk or fork, mix until well combined. Set aside.

In a large bowl, add in butter, vegetable oil and sugar. Using an electric mixer, cream together for 2 minutes until light and creamy.

Add in eggs one by one, mixing well in between each addition.

Add in egg yolks and mix until well combined.

Add in vanilla, vinegar and buttermilk and mix until well combined.

Finish off by adding in your premixed dry ingredients to your wet mixture, and gently fold with a spatula until just combined.

Distribute the batter evenly into the two 8 inch cake tins. Drop the cake tins lightly on the counter to remove any large air bubbles and bake for 38-40 minutes or until a toothpick comes out clean or with a few moist crumbs on it.

Once baked, allow the cake layers to cool in the cake tins for 20 minutes, before turning them out onto a wire rack to completely cool.

In a microwave safe bowl add in chocolate and melt in the microwave for 30 second bursts at a time, mixing in between each burst until the chocolate is almost melted. Let the chocolate sit for a few minutes and then mix until smooth. Set aside to cool.

In a large bowl, add in butter, powdered sugar, vanilla and heavy cream. Mix on the lowest speed until the ingredients are combined, and then turn up the speed to a medium high and mix for a full 10 minutes.

Add in the cocoa powder and cooled melted chocolate. Mix until well combined and smooth.

Trim off the tops of the cake layers with a serrated knife so that they're nice and flat.

Place the first cake layer onto a serving plate/cake stand and spread out a generous amount of frosting.

Place the next cake layer on top and spread out more frosting on the top and sides of the cake.

Using a 1M piping tip, pipe some cupcake swirls on the top of the cake. Slice and enjoy!