Spray parchment paper on cookie sheet with cooking spray. Preheat oven at 325.
Beat egg whites, salt and cream of tartar until foamy, add sugar gradually until mixture is satiny, then add vanilla. Beat for about 15-20 minutes until stiff peaks form. It takes a little while, but once you've reached the consistency of marshmallow creme, you're good to go.
Drop tablespoonfuls onto cookie sheet and bake about 30-35 minutes or till light brown. Allow puffs to cool before removing from cookie sheet, otherwise the bottoms will break off (they're very fragile cookies since they're basically full of air).
To flavor puffs: for chocolate: omit vanilla sugar, add 1 tsp. chocolate syrup or other extracts instead, or add 1/4 cup of the following: chocolate chips, dried fruit, walnuts, or whatever you please. We enjoyed these, and they are easy to make and tasty all year round (and not too fattening)!