Preheat the oven to 350F (180C) degrees.
Line the bottom of two 8-inch round cake pans with parchment paper. Lightly grease the sides and dust with cocoa powder. If using 8-inch round pans, make sure that the sides are at least 2 inches (about 5 cm) high. See recipe notes for pan options.
In a very large bowl, whisk together the flour, cocoa, baking soda, baking powder and salt.
In a separate large bowl, whisk together the buttermilk, eggs and vanilla extract.
Carefully whisk the wet ingredients into the dry ingredients until smooth and no lumps remain.
Carefully whisk in the hot coffee until the mixture is smooth and an even consistency. It will be thin.
Pour the batter into the prepared pans.
Bake in the preheated oven for about 30-35 minutes on the same rack, or until an inserted toothpick comes out clean and you see the cake starting to pull away from the sides of the pan. Baking times vary, so go by your toothpick test and not just the stated time.
Place cakes on a wire rack to cool. Keep cakes in the pans until fully cooled