10 egg whites, room temperature
2 tsp vanilla extract
1 1/2 tsp cream of tartar
1 teaspoon salt
2 cups firmly packed light brown sugar, divided
1 1/4 cups sifted cake flour

Beat egg whites and vanilla together in a large mixing bowl on high just until foamy. Add cream of tartar and salt. Beat until soft peaks form. (Soft peaks will curl over slightly.) Press 1 cup of brown sugar through a wire mesh sieve the sprinkle over the egg white mixture. Beat until stiff peaks form. Sift together remaining sugar and cake flour. Gently fold the sugar and flour mixture into the egg white mixture a little at a time. Pour into an ungreased 10-inch tube pan. Bake in a 350 degree oven for 45 to 50 minutes, or until cake springs back when lightly touched. Invert pan and cool completely. Loosen the cake from the sides with a knife or narrow metal spatula