1) Preheat oven to 350 degrees.
2) Place oven rack in center of oven.
In a large mixing bowl, combine the egg whites, salt, and cream of tartar. Using an electric hand mixer, beat on medium speed until frothy. Add the vanilla extract and lemon juice. Beat on high speed until soft peaks form. Gradually add the powdered sugar and beat until the mixture forms stiff peaks. Sprinkle the cake flour over the egg white mixture. Using a spatula, carefully fold in the flour until incorporated. Spoon the batter into an ungresed 10-inch nonstick angel food cake pan.
Bake for 30-40 minutes until the top is browned and a skewer inserted halfway between the inner and outer wall of the pan comes out clean. Invert the pan on wire rack to cool completely, about 1 hour.