Sift sugar and flour together. In a sauce pan, mix the butter, cocoa and water bringing to a rapid boil. Pour over flour and sugar mixture and stir until well mixed. Add buttermilk, eggs, baking soda cinnamon and vanilla. Mix well and pour into a greased pan that's at least 1/4" and bake at 400* in preheated oven for 20 minutes.
Begin making about 5 minutes before the cake is done.
Melt butter, cocoa and buttermilk together and bring to a rapid boil. Remove from heat and add 1 box of powdered sugar, vanilla and pecans. Beat well with spoon and spread on the cake while it's hot.