Mix the flour, 2 cups of the sugar, baking soda, 6 tablespoons of the cocoa, salt, vegetable oil, vinegar, 2 teaspoons vanilla, and the water together. Stir until just combined. Pour batter into on ungreased 13x9 inch baking pan.
Bake at 325 degrees F (165 degrees C) for 30 to 35 minutes. Let cake cool than ice.
To Make Icing: Beat together the butter or margarine, vegetable shortening, 1 cup sugar, milk, and 1 teaspoon vanilla. Continue beating for 10 minutes. Spread over cooled cake.