Anna's Angel Food Cake

1. Preheat the oven to 180°C.
2. Sift the flour and granulated sugar twice and set aside.
3. Whip the egg whites with the cream of tartar and salt until foamy, then gradually add the icing sugar, whipping until the whites hold a medium peak when the beaters are lifted. Stir in the vanilla. 
4. Add the flour to the whipped whites in 2 additions and using a whisk to fold in the flour evenly and easily. Scrape the batter into a 10-inch ungreased tube pan, spread it to level and bake the cake for 30-35 minutes, until it springs back when gently pressed (try not to open the oven before 25 minutes).
5. Turn the cake pan upside down to cool the cake, and do not remove the cake from the pan until completely cooled. To remove, run a palette knife carefully around the outside of the cake, and very gently around the inner tube, invert the pan and tap it on the counter until it comes out.
6. Serve the cake with whipped cream and berries, if you wish.

The cake will keep, well wrapped (not refrigerated) for up to 3 days.