Preheat the oven to 350 degrees. Line a jelly roll pan with parchment paper, or spray well with nonstick spray.
To a saucepan, add butter, water, coffee, and unsweetened cocoa powder. Bring to a boil then remove from the heat. Let it cool then stir in brown sugar vanilla.
In a bowl, combine all-purpose flour, sugar, salt, and baking soda. Whisk together to combine dry ingredients.
Add dry ingredients into saucepan. Stir well, then add sour cream and eggs. Blend well until lumps are gone.
Pour the batter into the pan and spread evenly to the sides. Bake for about 18-20 minutes, or until a toothpick comes out clean.
To a clean saucepan, add butter and cocoa. Stir until it boils, then remove from the heat and whisk in sour cream and vanilla extract and powdered sugar.