Preheat oven to 350°F. Spray an 8x8 inch or 9x9 inch baking dish with nonstick spray.

In a large mixing bowl, combine flour, sugar, salt, baking soda, and cocoa powder. Stir to mix.

In a measuring cup, combine vinegar, water, and vanilla. Stir, then add to the dry mixture along with the oil. Stir the batter to mix, scraping sides as needed.

Pour the batter into the prepared pan and bake for 35 minutes or until a toothpick inserted in the center comes out clean. Allow cake to cool completely before icing.

Prepare the icing by combining powdered sugar, cocoa, and vanilla in a medium bowl. Add 2 tablespoons of water and stir until thick but pourable. Add more water if needed.

Pour the icing over the cooled cake and spread evenly. Serve and enjoy!