Preheat oven at 180C. Prepare a 8" or 9" cake tin by creasing with oil and dusting with flour.
Add 1 cup water into a mixing bowl. To that add 1 cup sugar. I have sued castor sugar here. You can any type of powdered sugar. Mix well to dissolve the sugar.
Add 1/4 cup oil, 1 tablespoon vinegar, 2 teaspoons vanilla extract. Mix the wet ingredients thoroughly.
Sieve wheat flour, plain flour, salt and baking soda over the wet ingredients. Fold and mix.
Pour the prepared batter into the greased and dusted tin. Tap once or twice.
Bake for 30-40 minutes depending up on your oven. The cake is done when the top cracks a bit and a tester comes out with very few crumbs.
Let the cake cool for 10 minutes in the pan. Then invert and cool in a wire rack till it reaches room temperature.
You can dust with sugar or cocoa powder if needed.
Cut the cooled cake into squares and serve as snack or dessert.