In an extra large mixing bowl allow egg whites to stand at room temperature for 30 minutes. Meanwhile, sift powdered sugar and flour together 3 time; set aside.
Add cream of tartar and vanilla to egg whites. Beat with an electric mixer on medium speed till soft peaks form (tips curl). Gradually add granulated sugar, about 2 tablespoons at a time, beating till stiff peaks form.
Sift about one-fourth of the dry mixture over beaten egg whites; fold in gently. (If bowl is too full, transfer to a larger bowl.) Repeat, folding in remaining dry mixture by fourths. Pour into an ungreased 10 inch tube pan. Gently cut through batter to remove any large air pockets.
Bake on the lowest rack in a 350 degree oven for 40 to 45 minutes or till top springs back when lightly touched. Immediately invert cake (leave in pan); cool thoroughly. Loosen sides of cake from pan; remove cake.
Tip: Turn cake upside down immediately after baking and let cool completely. If your cake is too high, invert the pan over a metal funnel or a glass bottle that has a slim neck.
Tip: Loosen the cooled cake from the pan by sliding a metal spatula between the two. Constantly pressing the spatula against the pan, draw it around the pan in a continuous, not sawing, motion so you don't cut into the cake.