Preheat oven to 350 degrees. Spray a 12cup Bundt pan or tube with cooking spray. Dust the pan with some flour and shake out the excess. In a large bowl, whisk together the flour, sugar, cocoa, baking soda, baking powder and salt. Add the buttermilk, brown sugar, eggs, oil and vanilla. Beat with an electric mixer on high for 2 minutes. Whisk in the hot coffee. Pour the batter into the pan and bake for 45 to 50 minutes until the tester comes out clean. Cool the cake in the pan, then invert the cake onto a wire rack to cool completely. Icing: In a bowl, whisk sugar, vanilla and enough of the milk to make a thick icing but thin enough to drizzle on the cake and have it run down the sides.