This cake is so quick and easy to make because it can be mixed right in the 8-inch square pan. Do NOT grease the pan. Mix flour, sugar, cocoa, baking soda and salt with a whisk until well blended. Pour the oil, vinegar, vanilla, and cold water (all at once) on top of the dry ingredients. Stir until all the ingredients are thoroughly blended together but do not over-mix. Bake at 350°F for 35 to 40 minutes or until a toothpick inserted in the center comes out clean.