Preheat oven to 325°. Line a sheet pan with parchment paper. Prepare a pastry bag with a large tip. Beat egg white, cream of tartar, vanilla extract and salt with mixer using whisk attachment until foamy. Slowly add sugar, a few tablespoons at a time beating on high until all sugar is dissolved and stiff peaks form.
Fill a pastry bag 2/3 full with mixture and pipe single circular swirls onto parchment paper. Bake for about 35 minutes or until crisp, being careful to remove before the bottoms begin to burn. cool on wire rack.
You can substitute any flavoring extract, such as orange, licorice, or mint. You can also add a few drops of your favorite food coloring to personalize your cookies.
Note: If you don't have a pastry bag but have a tip, you can use a large zip-lock bag and cut a corner off and attach the pastry tip and coupler. Trust me, the store brand zipper freezer bags are much cheaper than buying the disposable pastry bags and they work just as well. If you don't have a pastry tip at all, then drop the mixture onto the parchment with a spoon.