Preheat the oven to 350. Sift together 1/2 cup of sugar and the cake flour, and set aside.
In a large bowl or the bowl of a stand mixer, beat together the egg whites, cream of tartar, vanilla, and salt until soft peaks form. Add the remaining cup of sugar, a few tablespoons at a time, while beating on high speed, until stiff peaks form. Fold in the flour and sugar mixture gently, being careful not to deflate the egg whites.
Gently scoop the cake batter into an ungreased 10 inch tube pan. Run a knife through the batter to remove air bubbles. Bake 35-40 minutes, until golden brown on top. Turn the pan upside down to cool and allow to cool completely.
When ready to serve the cake, run a knife around the edges of the pan to release the cake. Dust with powdered sugar, and top with fresh berries.