Preheat oven to 160 °C (320°F) with the fan on (see note 5 if you don't have a fan function) and grease and/or line two 8 inch cake tins (I use my homemade cake release). In a bowl, sift together your flour, cornflour, baking soda, baking powder, salt, instant coffee powder and cocoa powder. Using a whisk or fork, mix until well combined. Set aside.
In another bowl, add in your butter, vegetable oil and sugar. Using an electric mixer (hand or stand mixer are both fine - see note 2), cream together for 2 minutes until light and creamy.
Add in eggs one by one, mixing well in between each addition (about 10-15 seconds between eggs).
Add in your vanilla, vinegar and half a cup of the buttermilk, and mix until well combined. Now set your mixer aside as the remainder of the batter will be finished by hand.
Finish off by adding in half of your premixed dry ingredients to your wet mixture, and gently fold it in with a spatula until just combined. Then add in the remaining 1 cup of buttermilk, and fold it in until just combined. Lastly, add in the remaining dry ingredients and gently fold it into the mixture until just combined. Do not overmix (see note 3).
Distribute the batter evenly into the two 8 inch cake tins, and bake for 40 minutes or until a toothpick comes out clean.
Once baked, allow the cake layers to cool in the cake tins for about 15-20 minutes, and then turn them out onto a wire rack to completely cool before frosting with the chocolate cream cheese buttercream recipe below, or another frosting of your choice.