Preheat the oven to 350 degrees F.
Place the sugar in a food processor and process until it is finely ground. Divide the sugar in half. Combine one half with the flour, leavening agent and salt and place in a sifter.
Combine the egg whites, 1/3 cup room temperature water, cream of tartar and vanilla. Place in the bowl of the standing mixer. Start on slow for 2 minutes, and then increase the speed to medium. Slowly add the remaining sugar to the egg whites and continue to mix.
Once the egg whites are at medium peaks, remove the bowl from the mixer and sift over the flour mixture a little at a time as you fold it together. When completely combined, transfer to a 10-inch ungreased angel food cake pan. Transfer to the oven and bake for 35 minutes.
Remove from the oven and invert while still in the pan. Let cool for at least an hour upside down.
Insert a knife around the edges and remove from the pan. Serve.
Recipe courtesy of Scott Conant