Add the flour to a sifter, and sift it into a large mixing bowl.
To the same mixing bowl add the sugar, salt, baking soda, and cocoa powder. Whisk them together until evenly combined.
To a small mixing bowl, add the water, vanilla, and vinegar. Set aside.
Pour the oil into the large mixing bowl with the combined dry ingredients. Stir briefly.
Give the water mixture another stir to combine, and then pour it into the large mixing bowl. Whisk together until the batter's almost completely smooth. Scrape the sides and bottom of the bowl, as necessary, to make sure the batter's completely mixed.
Lightly spray an 8x8" square baking dish with non stick cooking spray, and then pour the batter into the dish. Use a spatula to scrap down the bowl, getting all of the batter into the dish. Use the same spatula to gently spread the batter out evenly into the baking dish.
Bake the cake at 350° for 35 minutes. Insert a wooden skewer into the center of the cake, and if it comes out clean the cake is cooked throughout.
Set the chocolate cake aside to cool. You can serve it warm, or wait until it cools completely and add the chocolate ganache.