In medium pan 2 sticks of butter, 1/3 cup cocoa and 1 cup of water. Cook at medium heat, stirring occasionally until it begins to boil. Pour over sugar and flour mixture; mix well. Add 2 eggs, 1/2 cup buttermilk, 1 teaspoon of baking soda and 1 teaspoon of vanilla; mix well. Pour into sheet cake pan (sprayed with Pam) and bake at 400 degrees for 20 minutes. Leave in pan. Start making icing last 8 minutes of cake baking. Sheet cake pan 11 x 15 1/2 inch.