Preheat the oven to 325 degrees and move the racks so one is in the lower middle.
Pulse the sugar until it is fine but not powdered, set one cup of the sugar aside.
Add the tapioca starch, potato or corn, starch, cassava flour, and salt and pulse again to help combine and aerate the dry ingredients to the remaining sugar still in the food processor.
Add the egg whites to a bowl (I use my stand mixer) and the cream of tartar on medium-low speed until the mixture becomes foamy.
Once the eggs are foamy, slowly add the sugar that was set aside while mixing over medium speed.
When all the sugar is combined, continue to beat the eggs until they form soft white peaks. Remember not to take the egg whites any farther, so watch them.
Slowly and carefully add and fold in the dry ingredients in small batches to the egg whites until they are all added.
Pour and lightly spread the cake batter into the dry tube pan. You can lightly move the bowl back and forth to help level out the top if needed.
Bake the angel food cake in the middle of the oven at 325 degrees for 35-45 minutes. The cake will rise above the top, and it will have a golden brown color on top when it is done.
Remove the cake from the oven and carefully turn the cake upside down over a metal cooling rack. Do not let it stay upright for long, so it doesn't collapse.
Allow the cake to cool upside down until it's completely cool. I usually leave it alone for 2-3 hours.
When the cake is cooled, carefully run a knife around the edges of the pan and around the middle flute and give it a slight tap upside down to release the cake.
Slice the cake with a serrated knife and serve it alongside your favorite fresh berries, whipped cream, or whatever you desire.