The Most Delicious Angel Food Cake in the World!!! - Gluten Free

Angel Food Cake
14 egg whites
11/2 tsp cream of tartar
1/2 tsp. salt
2/3 c. granulated sugar
Sift next three ingredients:
1 c. powdered sugar
1/2 c. potato starch flour (Not potato flour)
1/2 c. cornstarch
In large glass or metal (Not plastic) mixing bowl, place egg whites, cr. of tartar, salt. Beat until mixture is well blended. Continue to beat adding granulated sugar slowly until sugar is dissolved & whites form stiff peaks.
With a rubber spatula gently fold in the 3 sifted ingredients about 1/4th at a time, folding just enough so the flour disappears.
Pour batter into ungreased 9" tube pan & cut through with spatula to break air bubbles.
Bake 35-40 minutes in preheated 360 - 375 oven ( I do 365) or until top springs back when lightly touched. Remove from oven & cook the cake in the inverted pan. Remove cake only when completely cool. Be sure there are no shiny white parts when it is done. It will fall out of the pan if not completely done.