Preheat the oven to 350 degrees and line muffin pans with cupcake liners. Mix together flour, baking soda, salt and cocoa in a bowl and set aside. In a mixing bowl, combine sugar and butter and beat on medium-high until light and fluffy.
Mix in the eggs one at a time, beating well after each and scraping down the sides if needed. In a small bowl, combine buttermilk, Coke and vanilla extract, making sure to let the foam calm down after you mix it in. Foam will do us no good here.