Pre heat your oven to 100℃ (212℉) -use convention setting, not fan-forced (see notes)
Line 1-2 baking sheets with silicone baking mats or baking paper (I use 2 large baking sheets)
In the mixer bowl of a stand mixer, place the egg whites and cream of tartar
Using a hand mixer on low to medium speed, whisk the egg whites until foamy and beginning to form soft peaks (I use the hand mixer first, as it's a small amount of egg whites and it's harder to whisk with the stand mixer at the start)
Place your mixing bowl onto your stand mixer and using a whisk attachment, whisk on low to medium, while slowly adding the caster sugar to the whipped whites, 1 tablespoon at a time (leave 30 seconds between each spoonful)
Once all of the sugar has been added, stop the mixer and scrape the side of the bowl with a silicone spatula
Now mix the meringue on medium speed for about 3 minutes, until it forms stiff peaks and is nice and glossy. Check that there are no large granules left, by rubbing a little of the meringue between your thumb and finger. You want a stiff, glossy meringue
Add the vanilla extract and food colour (if using) and whisk again until it’s combined. You will need to scrape the side of the mixing bowl with a silicone spatula, to ensure all of the colour mixes in
Transfer mixture to a large piping bag fitted with a large star tip, then pipe out your Meringue Christmas Trees -I pipe a little of the meringue onto the baking sheet, then pop my lollypop stick on top of it. This stops the stick from rolling around. Once in place, you can then pipe your Christmas Trees, starting at the top (just above the top of the stick) and working your way down, piping the meringue into a Christmas tree shape.
Use a spoon to add sprinkles to your meringue
Bake in the oven for 2.5 hours
Turn off the oven and leave the meringues to cool, with the oven door slightly ajar