Preheat the oven to 350 degrees. Grease and flour a 10-12 cup capacity bundt pan with butter or use Baker's Joy spray. Set aside.
Place cocoa powder and coffee in a small saucepan and bring to a boil, whisking constantly. Remove from heat and allow to cool.
In the bowl of a mixer, combine sugar, salt, baking soda, eggs, and yolk. Beat on low speed for about 1 minute. Add buttermilk, oil, and vanilla and beat for another minute or so.
Add flour to sugar mixture and beat on low speed for 30 seconds, then medium speed for about 2 minutes, scraping the bowl once. Add the cooled cocoa/coffee mixture and beat on low speed for another minute. Scrape the bowl to make sure everything is well mixed.
Pour into the greased pan and bake for about 1 hour, or until a toothpick inserted in center comes out clean. Let the cake cool at least 15 minutes before inverting onto serving tray.