Sift together the cake flour with 1/2 cup (95g) superfine sugar in a small bowl. Set aside.

In the bowl of a stand mixer with a whisk attachment, beat the egg whites on medium-low speed until foamy. Then add the cream of tartar and salt, and increase the speed to medium-high. Continue to beat until soft peaks form.

Gradually add the remaining 1 cup (190g) of sugar. Continue to beat on medium-high speed until stiff, glossy peaks form. The egg white mixture should hold its form on the whisk.

Add the vanilla extract to the egg white mixture and gently fold in with a spatula.

Sprinkle the sifted flour mixture over the egg white mixture in small batches. Gently fold in each addition until just combined. Be careful not to deflate the mixture by over mixing. 

Spoon the batter into an un-greased angel food cake pan. Use a spatula to smooth the top and gently tap the pan on the counter to remove any air bubbles.

Bake for 40 minutes, or until the cake top is golden brown and springs back when gently pressed. Remove the cake from the oven and immediately invert the pan onto a wire rack. Let the cake cool completely upside down in the pan to avoid collapsing the cake. 

Once completely cooled, run a knife around the edges of the pan and remove the cake from the pan.

Serve slices of angel food cake with fresh berries and whipped cream, if desired.