Preheat your oven to 350°F (175°C) and grease a round cake pan.

In a large mixing bowl, combine the cocoa powder, flour, sugar, baking soda, and salt. Whisk until well combined.

Add the softened butter to the dry ingredients and mix until the texture is crumbly.

In a separate bowl, whisk together the eggs, buttermilk, whiskey, and vanilla extract.

Gradually pour the wet mixture into the dry ingredients, stirring just until everything is well incorporated. Be careful not to over-mix.

Pour the batter into the prepared cake pan and smooth out the top.

Bake for about 25-30 minutes, or until a toothpick inserted into the center comes out clean.

Once done, let it cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.