Preheat oven to 350 degrees. Line a cupcake tin with cupcake liners, set aside.
In a food processor, place the sugar and pulse until very fine, about 2 minutes. Sift half of the sugar with the flour and salt, set aside.
In a large bowl with a hand mixer or a stand mixer, add the egg whites, add in the water, vanilla and cream of tartar. Mix on low until fully combined. Gradually add in the remaining sugar until incorporated. Place mixer on medium speed until egg whites form medium peaks.
Start to add in the flour mixture a little at a time by sifting it onto the surface of the egg mixture and folding it in in very small batches by hand.
Fill the cupcake liners almost all the way to the top, about 3/4 full. Bake for 16 to 18 minutes or until a toothpick inserted into the middle comes out clean. Let cool for 5 minutes in the tin, then transfer to a wire rack to cool completely.