Mix flour and 1/2 cup sugar in small bowl. Set aside.
Place egg whites in mixer bowl. Attach bowl and wire whip to mixer. Gradually turn to speed 6 and whip 30 to 60 seconds, or until egg whites are frothy.
Add cream of tarter, salt, and vanilla. Turn to speed 8 and whip 2 to 2 1/2 minutes, or until whites are almost stiff but not dry. Turn to speed 2.
Gradually add remaining 1 cup sugar and mix about 1 minute. Stop and scrape bowl.
Remove bowl from mixer. Spoon flour-sugar mixture, one-fourth at a time, over egg whites.
Fold in gently with spatula, just until blended.
Pour batter into UNGREASED 10-inch tube pan. With knife, gently cut through batter to remove large air bubbles. Bake at 375 for 35 minutes, or until crust is golden brown and cracks are very dry. Immediately invert cake onto funnel or soft drink bottle. Cool completely. Remove from pan.