Sift the flour, sugar, cocoa, baking soda, baking powder, and salt into the bowl of an electric mixer fitted with a paddle attachment or a large mixing bowl. Mix on low speed until combined. In a separate medium bowl or large measuring cup, whisk together the buttermilk, oil, eggs, and vanilla. With the mixer on low speed, slowly pour the wet ingredients into the dry. With the mixer still on low, add the coffee and continue mixing, just until combined. The batter will be very thin.
Place rack in the upper third of oven and preheat the oven to 350 degrees F. Lightly coat a a standard 12-cup muffin tins with cooking spray.