Generously grease an 8 inch loaf pan, and preheat your oven to 350 degrees. (see notes for other baking options)
In a large bowl, whisk together the flour, sugar, cocoa powder, espresso powder, salt, and baking soda. In a medium bowl, stir together the vanilla extract, white vinegar, oil, and water.
Pour the wet ingredients into the dry mixture, and whisk to combine until completely smooth. The batter will be fairly thin. Pour into your prepared baking pan, and sprinkle with able a tablespoon of coarse sugar (optional).
Bake for 50-55 minutes, or until a cake tester comes out clean. Cool before removing from pan and serving.
In a small saucepan, stir together the sugar, cocoa, and water until combined. Cook over medium heat until it reaching a rapid boil. Pour into a heat-safe container to cool until the cake is cooled. The sauce will be very thin, but it thickens as it cools. Drizzle over the cake before slicing and serving. Enjoy!