Preheat oven to 350 degrees (175 degrees C). Spray one 13×9 inch cake pan with cooking oil spray.
Mix the flour, white sugar, 4 1/2 tablespoons cocoa, baking soda and salt together in a bowl. Pour dry ingredients into the prepared pan. Scoop out 3 holes in the dry mixture. Put the vegetable oil in one hole, vinegar in the second hole, and 1 1/2 teaspoons of the vanilla in the third hole. Pour the cold water over the top and stir until smooth.
Bake at 350 degrees F (175 degrees C) for about 20 minutes. Ice cake while it is still hot.
To Make Icing: In a saucepan over medium heat melt the butter or margarine. Add the cocoa and remove pan from the heat. Stir in the salt, milk and 1 teaspoon vanilla. Mix in the confectioners’ sugar until desired consistency is attained. Spread icing over a still hot cake.
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