Preheat the oven to 220°F (105°C). Line a baking tray with parchment paper. Set aside.
Add the egg whites and cream of tartar to the bowl of your stand mixer. Starting at slow speed, gradually increase to medium speed until the mixture becomes foamy.
Increase the speed to high and let it whip until white and creamy.
Start pouring in your sugar slowly, while the mixer runs.
Add in your vanilla extract and keep whipping until you have stiff peaks and a very thick marshmallow like texture.
Add in your food coloring if you're using it and whip it again briefly to spread the color through.
Add the mixture to a piping bag and pipe it out onto the prepared baking tray. The cookies can be quite close together as they don't really spread much when baking.
Bake for an hour and then switch off the oven, but don't open the door. Let them sit in the oven for another hour before removing them from the oven.