Well they're not really cookies as such, but you can pick them up with one hand and eat them so 'cookies' will do for me.
Start off by preheating the oven to 100C (80C for fan assisted) and beat four egg whites until stiff peaks form. I used a stand mixer but you could use an electric whisk or even do it by hand if you're feeling energetic.
Once the eggs are stiffly beaten, whisk in 250g caster sugar and beat until the meringue is glossy.
Next put the meringue mixture into a piping bag (it really is easier to do these in a piping bag rather than trying to spoon it onto the tray and make a tree shape).
Line a baking sheet with parchment paper or silpat and pipe Christmas tree shapes by zigzagging back and forth.
You can pipe these really close together because meringues don't spread.
Now pop the tray in the oven and basically forget about them for two hours. It doesn't really matter what size you make the trees, it'll still take about two hours.
Once they're ready take the tray out of the oven and lift the trees straight off to cool down. They actually only take about ten minutes to cool so you can spend the time getting your decorations together.
Yes, there is a sneaky snowman up in the top left corner:)
We used blue and pink icing 'tinsel' on our trees, but you could use anything really. Dip them in chocolate (but wait til it cools a fair bit), cover in sprinkles add a shake of edible glitter or sandwich two together with fresh cream and strawberry jam in the middle, anything goes really with meringue.
And enjoy them.
With 20/20 hindsight, I should have been making these all year. You can freeze them undecorated, they keep for months and months in the freezer and they're a great way to use up any eggs that are close to their best before date because old eggs make better meringue than fresh.
I should plan ahead more next year.