1. Prepare the Crust:

1. Preheat oven to 200°F (95°C) and line two baking sheets with parchment paper.
2. In a very clean, grease-free bowl, beat the egg whites and cream of tartar on medium-high speed until soft peaks form. Gradually add the sugar, a tablespoon at a time, and continue beating until the meringue is thick, glossy, and holds stiff peaks. Beat in the vanilla extract.
3. Add a few drops of green gel food coloring and gently fold until the color is uniform and streak-free. Fit a piping bag with a star tip and fill it with the green meringue.
4. Pipe tree shapes onto the prepared baking sheets by starting with a wide base and moving the tip upward to create a pointed top. Bake for 1.5 hours, then turn off the oven and let the cookies cool completely inside for another hour.