In a 23 centimeter / 9 inch round, 20 centimeter / 8 inch square or 23 x 15 centimeter (9 x 6 inch) rectangle baking pan, combine flour, cocoa, baking soda, salt and sugar. In a bowl, combine water, oil and vanilla. Pour liquid into dry ingredients, whisk with fork to combine. Add the vinegar - stir only until the vinegar is distributed around the batter (color variations will occur because of reaction with vinegar and baking soda - not a problem). Bake for 25-30 minutes. You can serve with spoonful of applesauce to make it like a german sacher torte.