Special equipment: a large pastry bag fitted with a large star tip
Preheat the oven to 200 degrees F; line 2 baking sheets with parchment paper.
In a stand mixer fitted with a whisk attachment, add the egg whites, vanilla and cream of tartar. Beat until the mixture is frothy and soft peaks form. Gradually add the sugar 1 tablespoon at a time, waiting about 15 seconds between each addition. Once all of the sugar has been added, beat for an additional 5 minutes. The egg whites should be glossy and stiff but not dry.
Spoon the mixture into a large pastry bag fitted with a large star tip. Pipe 2-inch cookies onto the lined baking sheets, leaving 1 inch between each cookie.
Bake for 45 minutes, then turn off the oven and leave the cookies in the oven for an additional 30 minutes. Remove and cool completely before storing in an airtight container.