Pre-heat the oven to 175ºC (350ºF) and grease a muffin tin (6 holes).
Beat the icing sugar and butter together for several minutes until light and fluffy (I used my food processor).
Add the vanilla extract and beat quickly again. Add the flour and continue to work until the mixture pulls together as a dough.
Divide the dough into six, equal sized, pieces and then with your hands, roll them into balls. Place them in the prepared muffin tin. Push down a little, but not too much (they will spread to fill the holes).
Bake for 12 minutes, until the tops are just starting to turn a little brown. The cookies will be very pale, but that's perfect.
As soon as they come out of the oven, find something to make the holes in the cookies. I use a measuring spoon, but you could use a small glass, or anything else that is an appropriate size.
Press down in the middle of the cookies (making sure you don't go all the way to the bottom) and give whatever you are using a little wiggle to increase the size of the hole.
Allow the cookies to cool completely before attempting to take them out of the muffin tin. If you do it too soon, they will crumble.