Preheat your oven to 170°C/340°F (150°C/300°F with fan).
Prepare a 20cm (8inch) square pan with baking paper or non-stick oil spray.
Add your sugar, eggs and vanilla to a medium bowl. Mix until thickened and light and fluffy.
Drizzle the oil slowly into the egg mixture while mixing and mix until well combined.
Sift flour, cornstarch, baking powder and salt into the egg mixture. Fold in gently making sure you don't lose too much air that has been whipped into the egg mixture.
Pour and even out your mixture in your prepared pan.
Bake for about 25-30 minutes until a skewer or toothpick comes out clean. Don't open the oven to early or you risk the middle falling flat.
Let cool completely before dipping.