Sift sugar and plain flour together in a large bowl.
Mix together butter, cocoa and water in boiler and bring to boil; pour this mixture over the flour and stir well.
Add eggs and soda dissolved in buttermilk; mix well.
Add cinnamon and vanilla; mix well by hand and pour into a greased 9x13" pan. (Glass pan is best.)
Bake at 400 for 20-25 minutes.
Chocolate Fudge Icing: Melt together and boil cocoa, butter and milk; add powdered sugar, vanilla and pecans.
Spread icing over cake in pan and cut into squares.