Before I forget it. There'll be a post to put this in context eventually.
1 egg white
1/4 tsp cream of tartar
~150g icing sugar
Whisk for a while until it's smooth and very thick (the recipe I was using said 7 minutes, I got impatient).
If you can't find your icing bag or tips (speaking hypothetically, of course), cut the corner off a small zip-lock bag (I find regular plastic bags too thin, plus with the ziplock it's easier to store some for later).