Add the cream of tartar, salt and vanilla to the egg whites. Using the whisk attachment, beat on medium speed until soft peaks form. Gradually add the remaining 1/2 cup sugar, 2 tablespoons at a time. Beat on high speed until it forms stiff peaks.

Using a rubber spatula, gradually fold in the dry ingredients 1/2 cup at a time.

Spoon the angel food cake batter into an ungreased 10-inch tube pan. Gently swirl a knife through the batter to remove air pockets.

Bake at 350 degrees on the lowest oven rack for 40-45 minutes, or until the top of the cake is lightly browned and looks dry. If the top springs back it is done.

Remove the pan from the oven and immediately invert pan, standing it upside down on 3 glasses that are equal in height for support.

Let the cake cool upside down for one hour.

Slide a knife around the sides of the pan to loosen the cake.