Turn oven to 180 C. Grease a 20cm tin well. Dust inside the tin with a little flour. Tap out excess. Put the flour, sugar, cocoa and water in a bowl. Add vanilla, vinegar, oil, baking soda and salt. Mix with beaters until smooth. (Mixture is runny.) Pour into the tin. Bake 35 to 40 minutes. Cool for 10 minutes then take out of tin. Ice with your favourite icing.