Preheat oven to 350.
Mix flour, sugar and soda in a bowl.
Bring butter, water and cocoa to a boil in saucepan. Pour over dry ingredients. Mix thoroughly.
Add buttermilk, eggs and vanilla. Beat well.
Pour into a greased 9 x 13” pan and bake at 350 degrees for 30 minutes or until it tests done.
Heat butter, cocoa and buttermilk just to boiling. Remove from heat and mix in vanilla, sugar and nuts.