In a large bowl, whisk the sugar, buttermilk, oil, egg, and vanilla together until smooth. In a medium bowl, sift the flour, cocoa and baking soda together and add to the buttermilk mixture, stir until the ingredients are just combined. Be careful not to overework the batter, If there are lumps, they will disappear during baking baking. The less you work the batter, the more tender the pies will be.
Fill 6 nonstick muffin top cups with the batter. Bake for 10 minutes in the center of the oven. To prevent the pies from getting soggy after baking, remove the cooked muffins from their cups and cool them on a rack. Serve warm.