Preheat the oven to 225°F and line a large baking sheet with parchment paper.
Pour the egg whites into a large, grease-free, dry bowl. Add in the cream of tartar, then start whisking. Mix at medium speed until frothy, approximately 2 minutes.
Add ¼ cup of the sugar, whilst mixing continuously for another 2 minutes or until the meringue reaches soft peaks.
Start adding in the remaining sugar gradually, whilst mixing over the course of 1-2 minutes. Once the sugar has been fully incorporated, add the vanilla.
Mix on high speed until the meringue reaches stiff peaks, around 2-3 minutes. Stop mixing once the meringue holds its shape well. Do not overmix.
Stir in the green gel food coloring, adjusting the color as desired.
Spoon the meringue into a large piping bag fitted with a ½ inch star tip.
On the prepared baking sheet, pipe one row of large star tip rosettes. Pipe a second row slightly smaller. Pipe a third row being the smallest. These will be the bottom, middle and top pieces of the tree.
Decorate with festive sprinkles, if using, then bake for 2 hours. Once baked, turn off the oven and open the door for 1 minutes. Shut the door and let the meringues cool down inside the closed oven for 1-2 hours.
Pop the rosettes off of the parchment paper. Place one of the largest rosettes on a workspace. Place a small dollop of vanilla buttercream in the center and top lightly with a medium rosette. Give it another small dollop and then finish with the smallest rosette.
This step is optional, but if you want to attach a small gold star to the top, do this with a small amount of buttercream. I used a toothpick to give it just a little "glue". Another favorite is a small dusting of powdered sugar for a freshly fallen snow look.
If you've tried this recipe, come back and let us know in the comments or ratings.