1Move oven rack to lowest position. Heat oven to 375ºF.
2Mix powdered sugar and flour; set aside. Beat egg whites and cream of tartar in large bowl with electric mixer on medium speed until foamy. Beat in granulated sugar, 2 tablespoons at a time, on high speed, adding vanilla, almond extract and salt with the last addition of sugar. Continue beating until stiff and glossy meringue forms. Do not underbeat.
3Sprinkle sugar-flour mixture, 1/4 cup at a time, over meringue, folding in just until sugar-flour mixture disappears. Push batter into ungreased angel food cake pan (tube pan), 10x4 inches. Cut gently through batter with metal spatula.
4Bake 30 to 35 minutes or until cracks feel dry and top springs back when touched lightly. Immediately turn pan upside down onto heatproof funnel or bottle. Let hang about 2 hours or until cake is completely cool. Loosen side of cake with knife or long, metal spatula; remove from pan.