In a food processor spin sugar about 2 minutes until superfine. Sift half of the sugar with the salt and cake flour, set aside the remaining sugar.
In a large bowl, use a hand mixer set to low to thoroughly combine egg whites, water, balsamic, and cream of tartar. After 2 minutes, increase speed to medium and slowly sift in the reserved sugar, beating continuously. Once you have achieved medium peaks, sift enough of the flour mixture in to dust the top of the foam. Using a spatula to fold in gently. Continue to sift and fold in until all the flour mixture is incorporated.
Carefully spoon mixture into an ungreased tube pan. Bake for 35 minutes and check for doneness with a wooden skewer by inserting halfway between the inner and outer wall; it should come out dry when cake is done.
Take cake upside down on baking rack and let cool for at least one hour before removing from pan.