Preheat the oven to 170°C. Grease a deep 30 x 20cm ovenproof dish or baking tin well with nonstick spray.
1. Sift the flour, baking powder, bicarbonate of soda and salt into a large bowl. Add the sugar and mix. Make a well in the middle.
2. In another bowl, whisk the water, oil, vinegar and vanilla essence then pour into the well in the dry ingredients. Beat until lightly mixed.