Preheat the oven to 375°F and prepare a 9x13 inch or 15x10-x1-inch baking pan with cooking spray.
In a medium bowl, whisk together sugar, flour, baking soda and salt.
Add the cocoa powder, butter and hot coffee/espresso to a small saucepan. Bring to a boil, stirring the entire time. Once the mixture starts to boil, remove from heat and add stir into the dry mixture and mix well.
Next, in a separate bowl, whisk the eggs, buttermilk and vanila together. Stir into the cocoa mixture until well incorporated. Batter will be very thin.
Pour batter into the prepared cake pan and bake for 20 minutes or until a toothpick entered into the center of the cake comes out clean. Let cool.