Preheat oven to 350 degrees. Have an ungreased 25 cm tube pan at hand. Combine cake flour and 1 cup brown sugar. In a large bowl, beat egg whites with cream of tartar and salt until foamy. Gradually add second cup of brown sugar. Continue to beat until stiff peaks form. Add vanilla; blend well. Divide flour-brown sugar mixture into 4 portions. Use a large rubber spatula to fold each portion in separately; gently lift meringue up and roll it over onto itself. Fold JUST until no traces of dry ingredients can be seen. Gently push batter into pan. With a long, sharp knife, make 5 or 6 vertical cuts through batter to get rid of large air pockets. Bake 45 minutes, or until top of cake springs back after it is lightly touched with a finger. As soon as cake is removed from the oven, IMMEDIATELY invert pan. If pan does not have legs, place the center tube over the neck of a large, heavy bottle. Do not remove from pan until cake is COMPLETELY cool...takes at least an hour. Dust with sifted powdered sugar, or frost with a favorite icing.

Here's an extra-ordinary cake with a delicate difference. Wis/Gramma.