Preheat the oven to 325°F (160°C).
Sift together cake flour and ¾ cup of sugar.
In a large mixing bowl with whisk attachment, beat the egg whites until foamy on a low speed.
Add cream of tartar and salt and continue to beat, gradually increasing the speed to high.
When the egg whites get whiter, add remaining ¾ cup of sugar one tablespoon at a time.
Add pure vanilla extract and continue to beat on high speed until hard peaks form.
Transfer the whipped egg whites into a large bowl.
Add flour/sugar mixture and carefully mix everything together. Be careful not to deflate the batter too much.
Now transfer the batter to ungreased angel food cake pan. Even out the surface. Run a butter knife through the batter to remove any air bubbles.
Bake for about 40-45 minutes. It’s ready if the inserted wooden stick comes out clean.
Cool the cake completely in the pan upside down for 90-120 minutes. This will make sure the cake stays soft and fluffy while cooling.