In the bowl of a stand mixer or a large mixing bowl with an electric mixer, add the egg whites.
Begin mixing and sprinkle in the cream of tartar and salt.
Beat on high until very foamy and soft peaks begin to form.
Slowly incorporate the sugar as you continue to whip on high.
Once the mixture is no longer translucent and stiff peaks form, check that the sugar has dissolved by rubbing a little bit between your fingers (if it's no longer grainy in texture the sugar has dissolved).
Then, beat the vanilla extract into the mixture for just a couple seconds.
Spoon the batter into a piping bag with a large star tip or other large pastry tip.
Pipe onto a baking sheet lined with parchment paper or a baking mat.
Bake at 225°F for 45 minutes.
Without opening the oven door, turn off the oven and allow the cookies to continue to bake and cool slowly for another 45 minutes.