Preheat the oven to 165 deg C, line a baking tray with parchment, the cookies will spread little so its good to have another tray as back up to bake them in two trays.
In a mixing bowl add the oil and sugars, whisk until pale and creamy using a whisk, electric beater or stand mixer.
Add the egg, vanilla and whisk again until smooth.
Add the dry ingredients and switch to a spatula to fold the ingredients together until thick and combined. We don’t want any dry pockets of flour.
Scoop out the dough into your palms and roll to form a ball. Dunk into castor sugar and roll around, dunk into the powdered sugar and roll again, place on the baking tray and repeat.
Bake for 10-12 minutes or until the edges are just set and the top has risen, cracked and puffy. I like them softer so under bake them, transfer to a wire rack to cool completely.
Serve with a glass of milk.