Preheat oven to 190 C / Gas 5. Grease a 20cm cake tin then line with baking parchment.
Mix the flour, sugar, baking powder and bicarb together in a mixing bowl (sifting isn't necessary). In a separate bowl whisk the oil, water and vanilla extract.
Make a well in centre of dry ingredients. Pour the wet ingredients into the centre, and mix well with a wooden spoon until well integrated, about 3 to 5 minutes. Pour the mixture into the prepared cake tin and let stand for at least 15 minutes. This step is essential for the gluten free flour to soak well.
Bake in the preheated oven for 45 to 60 minutes or until a skewer inserted into the centre comes out clean. Once ready, remove from oven and let cool for 5 minutes before turning out on a rack. Cool completely before filling and decorating as desired.