Preheat your oven to 160°C (320°F) with the fan function on. If your oven lacks a fan option, refer to note 5 for adjustments. Grease and line two 8-inch round cake tins with parchment paper or use a homemade cake release.

In a large mixing bowl, sift together the cocoa powder, all-purpose flour, cornflour, baking soda, baking powder, instant coffee powder, and salt. Whisk or stir with a fork to combine the dry ingredients evenly. Set this mixture aside.

In a separate mixing bowl, cream together the softened butter, vegetable oil, and granulated sugar using an electric mixer on medium speed. Beat for about 2 minutes until the mixture becomes pale and fluffy.

Add the eggs one at a time, mixing thoroughly after each addition for 10-15 seconds to ensure they are fully incorporated. Stir in the vanilla extract, white vinegar, and ½ cup of buttermilk. Mix until the wet ingredients are smooth and combined. Set the electric mixer aside for the next steps.

Using a spatula, fold half of the dry ingredients into the wet mixture gently, ensuring no lumps remain. Pour in the remaining 1 cup of buttermilk and mix lightly until just combined. Add the rest of the dry ingredients and fold gently until the batter is smooth. Avoid overmixing to maintain the cake's delicate texture (refer to note 3).

Evenly divide the batter between the prepared cake tins. Bake for approximately 40 minutes or until a toothpick inserted into the center comes out clean.

Allow the cakes to cool in their tins for 15-20 minutes before transferring them to a wire rack to cool completely. Only frost the cakes once they are at room temperature.

Using a hand or stand mixer with a paddle attachment, whip the softened butter on medium-high speed until it turns light and fluffy.

Gradually incorporate the powdered sugar in three additions, mixing on low speed between each addition. Ensure the sugar is fully combined before adding the next batch.

Add the cold, firm cream cheese and vanilla extract to the butter mixture. Beat just until the frosting is smooth and creamy. Avoid overmixing to prevent the frosting from becoming too soft (refer to note 4).

Finally, mix in the cocoa powder until it is fully blended and the frosting achieves a smooth, velvety consistency.

Use the frosting to layer and coat your cooled chocolate cake. Decorate as desired and serve. Enjoy!