Pre heat oven to 180℃/350℉ or 160℃ fan and line 2 trays with baking paper
In a medium bowl, beat the butter and icing sugar with a handheld electric mixer (you can also choose to do this with a stand mixer). Start on low speed and gradually increase to medium-high, beating until well combined.
Add the egg and vanilla paste, then beat again until mixture is creamy and smooth.
Whisk the cornflour, baking powder and salt into the flour, using a fork, then add the dry ingredients to the butter mixture.
Using the hand mixer, beat on low-medium until mixture is almost combined. Finish mixing with a silicone spatula, to avoid over mixing the dough.
Place mixture into the fridge for 10 minutes, to allow it to stiffen up. This will make rolling the cookies easier.
Using a large (3 tablespoon) cookie scoop, scoop out the mixture, rolling it into a ball, then placing onto the baking sheet before pressing it down slightly with the palm of your hand.
Bake for 15-18 minutes, until the cookies are no longer shiny, but haven't quite turned golden.
Allow the cookies to rest on the baking sheet for 5-10 minutes, then transfer to a cake rack to cool completely. Once cooled, make the frosting