In a planetary mixer with a paddle attachment beat the butter and shortening until pale and combined.
Add the white and brown sugar with the vanilla and beat until creamy and lighter in texture and color.
Add the egg and beat again until well incorporated and the mixture looks airy.
Sift the flour, corn flour, baking soda and salt over the bowl and cream the mixture on low speed until combined. Always scraping down the sides.
Using an Ice cream scoop portion the dough out onto a baking tray and set in the fridge for 1 hour minimum.
In a preheated oven at 170°C place 6 chilled cookie dough balls onto a lined 14x8 inch cookie tray with baking paper. They will spread while baking hence be mindful of the spacing.
Bake for 12-15 mins until the top is dry to touch and slightly risen. Remove and leave to cool on the cookie tray for a couple of minutes before transfer them to a wire rack to cool for 20 mins at least.
Store in an airtight container/jar at room temperature once completely cooled.