Preheat oven to 175°C. Line the bottom of 2 20cm (8 inch) cake pans with a minimum of a 5cm height (2 inch) with parchment paper. Spray the interior of the pan with cooking spray.
Into the bowl of your stand mixer fitted with the paddle attachment sift in all your dry ingredients; sugar, cocoa powder, baking powder, baking soda, and salt. Mix together on low just to combine. (If doing this manually sift all ingredients into a large bowl.
In a separate bowl whisk together buttermilk, eggs, oil, and vanilla.
With the mixer still on low slowly streams in the wet ingredients into the dry ingredients. Increase the speed of the mixer just until everything is properly combined. Scrape down the bowl (you can totally do this by hand as well just make sure to spend a good 2 min whisking the ingredients together to ensure a proper rise in the oven).
With the mixer on low add in your hot cup of coffee, and mix just to combine. The batter will have a very liquidy consistency.
Pour the batter evenly between the two prepared pans. To make sure your cakes bake with a flat top, cut up an old kitchen towel into thin strips the same height as your pan. Dip your towel strip into cold water and wrap the sides of your cake pans then secure with a pin (this reduces the temperature of the sides allowing the side and center of the cake to cook simultaneously and rise together).
Place in oven and bake for 35-40 minutes or until a toothpick inserted into the center comes out clean.
Remove the cakes from the oven and allow them to cool in the pans for 30 minutes. The edges of the cake should retract. Flip them out onto a cooling rack and allow them to continue to cool fully. Peel off the parchment paper.