Preheat your oven to 325 degrees F.
In a food processor, blitz granulated sugar until it becomes a powdery substance - about 1 minutes. After pulsing, it should measure approximately 2 cups. Remove 1 cup and set aside.
Whisk together cake flour, salt and 1 cup of blitzed sugar in a medium bowl. Set aside.
In the bowl of an electric stand mixer with the whisk attachment, whip egg whites and cream of tartar until there are no longer clumps of powder and gentle foam forms.
With the mixer on low speed, gradually add in remaining 1 cup of blitzed sugar and vanilla. Increase the speed on the mixer to medium to high speed and whip until medium to stiff peaks form.
Stop the mixer and remove the bowl from the stand. Fold in ¼th of the dry ingredients into the whipped egg white mixture. Do not stir the mixture - this is crucial to maintaining the airy batter. Repeat until all dry ingredients have been incorporated into batter.
Pour the batter into an ungreased tube pan. Gently shimmy the cake side to side to smooth the batter.
Bake for 40 minutes or until a toothpick comes out clean when inserted into the centre of the cake
Cool upside down on a cooling rack for 2 hours before removing from pan. Cooling the cake upside down is essential to maintaining the structure of the cake.