It's a really simple recipe and gives you a tasty cookie without much effort. I did end up changing the icing recipe, her's calls for meringue powder which is unavailable here. Changing the icing also let me switch the vanilla extract for peppermint giving the cookie an extra kick.
1 egg white
1 cup icing sugar
1/2 tsp peppermint extract
1/2 tsp green food colouring
Whisk everything until smooth adding the green food colouring until you're happy with the colour. If you have issues with egg whites (ie. you're pregnant) you should stick with her recipe but this one will work in a pinch.