Preheat the oven to 325°F. Grease one 8-inch round cake pan with non-stick spray, line it with parchment paper, and spray again. Set the pan aside.
In the bowl of an electric mixer fitted with a paddle attachment, combine the flour, sugar, cocoa, baking soda, baking powder, and salt. Mix on low speed until well combined.
In a separate bowl, whisk together the buttermilk, water (or coffee), oil, eggs, and vanilla.
With the mixer on low speed, gradually add the wet ingredients to the dry ingredients, scraping the bottom of the bowl with a rubber spatula as needed.
Bake for 25 to 30 minutes, or until a toothpick inserted into the center of the cake comes out with a few moist crumbs attached.
Allow the cake to cool in the pan for 10 minutes before turning it out onto a cooling rack. Let it cool completely, or serve warm with ganache.