Pre-heat the oven to 175ºC (350℉) and line a large baking tray with grease proof paper.
Cream the butter, vanilla and icing sugar together until fluffy.
Add the flour to the butter/sugar and mix just until a dough forms (it will be sticky).
Roll the dough out between two sheets of baking paper until it is thin.
Using a round cutter, cut circles out of the dough. For this particular recipe, I used a large cookie cutter, and ended up with 6 cookies, but you can use a smaller one and make more. Just remember that baking time might vary a little, depending on their size.
Bake for 8-10 minutes, just until the edges are starting to brown (keep a very close eye on them). They will look underbaked, but take them out or you will end up with overbaked cookies.
They will be very soft, so leave them on the tray for five minutes until they've hardened a little, then move to a wire rack and allow to cool completely.