Mix flour, sugar, soda. Set aside. Bring to boil butter, cocoa and water. Pour hot into dry. Mix well. Then add eggs, buttermilk and vanilla. Mix well.
Pour into greased jelly roll pan. Bake for 20 minutes at 350*.
Frosting; Bring to a boil 1 stick of butter, 4 T. cocoa, 6 T. buttermilk. Then add 1 box of powdered sugar or 2 1/2 cups. Add vanilla. Spread on cake while warm. ADd nuts if you like. My family like it without nuts.