Preheat oven to 350 F and line a cake tin with butter and dust with flour.
In a mixing bowl sift together flour, baking powder, baking soda, and salt. In another bowl add sugar and oil. Whisk until light and frothy. Stir in milk.
Add the flour into the wet mixture and gently fold in to combine.
Divide the batter into two bowls. Add vanilla extract into one bowl.Sift cocoa powder into one bowl of batter and add water.
Pour alternate tablespoons of vanilla and chocolate batter into the pan until all the batter finishes.
Bake in preheated oven fro about 30 minutes or until a skewer inserted into the centre comes out clean.
Remove from oven and cool the cake in the pan for few minutes.
Cool the cake, slice and serve.
Notes
Refrigerate or freeze the cake in cling wrap to store.