Preheat the oven to 225˚F and line 3 baking sheets with parchment paper or a silicone baking mat
In the bowl of an electric mixer, whisk together the egg whites and vanilla until foamy.
On medium speed, add the cream of tartar and whisk until the egg white mixture is white and just begins to stiffen. Gradually add the sugar, continuing to whisk, until the whites form stiff peaks and is shiny.
Add a few drops of food coloring and continue mixing until the desired color.
Pipe heaping tablespoons of the batter into a tree shape on the baking sheets leaving a couple of inches in between each cookie.
Top with a few sprinkles on each cookie.
Bake for 45-50 minutes and then turn off the oven and leave the cookies in the warm oven for an additional 20-25 minutes.
Cool completely on a wire rack and store in an airtight container.