Preheat oven to 350°F, and grease a 9-inch round cake pan.
Combine sugar, flour and cocoa in a large bowl. Stir in baking soda and salt.
Whisk in oil, vanilla and vinegar, and add water and mix until batter is smooth.
Pour batter into prepared pan. Bake 30 to 35 minutes until center is done and toothpick comes out clean.
Prepare optional glaze: Mix butter with 2 1/2 cups powdered sugar until creamy. Add vanilla and cocoa. Stir in 1/3 cup water until smooth. Mix in additional water for thinner frosting, or use more sugar to thicken the mixture. Cover and refrigerate until needed.
Allow cake to cool completely before frostng or serving. Enjoy!