Preheat your oven to 200 degrees Fahrenheit. Line two large baking sheets with parchment paper or silicone baking mats. Ensure that your mixing bowl and whisk attachment are completely clean and free of any grease or residue, as even a tiny amount of oil can prevent the egg whites from whipping properly.
Place the room temperature egg whites into the bowl of a stand mixer. Add the cream of tartar and begin whipping on medium-low speed until the mixture becomes foamy. Increase the speed to medium-high and continue beating until soft peaks form, which is when the whites hold their shape but the tips fold over when the whisk is lifted.
While the mixer is running on high speed, add the granulated sugar one tablespoon at a time. It is important to add the sugar slowly to allow it to dissolve completely into the whites. Continue beating until the mixture reaches stiff, glossy peaks. You can test this by rubbing a small amount of the meringue between your fingers, if it feels smooth and not gritty, the sugar has dissolved.
Gently fold in the alcohol-free vanilla extract and a small amount of green gel food coloring. Use a spatula to fold the color in until it is uniform, or leave it slightly streaky for a textured look. Be careful not to over-mix, as you want to keep as much air in the meringue as possible.
Fit a large piping bag with a star tip and fill it with the green meringue. To create the trees, pipe three layers of stars on top of each other. Start with a large star for the base, pipe a medium star directly on top, and finish with a small star to create a point. Leave about an inch of space between each tree on the baking sheet.
Carefully place your sprinkles on the trees to look like ornaments and add a gold star to the top of each one. Place the trays in the oven and bake for 90 minutes. Once the time is up, turn off the oven and leave the door slightly ajar, allowing the meringues to cool completely inside the oven for at least an hour. This prevents cracking caused by sudden temperature changes.
