1. Bring egg whites to room temperature.
2. sift powdered sugar and flour together.
3. in a large bowl beat egg whites, cream of tartar, and vanilla with an electric mixer on medium speed untill stiff peaks form (or tips stand straight)
4. sift about one-forth of the flour mixture over beaten egg whites; fold in gently
5. repeat; folding in remaining flour mixture by fourths.
6. pour into ungreased 10-inch tube pan.
7. bake on lowest rack in a 350 degree oven for 40 minutes or till top springs back when lighty touched
8. immediately invert cake (leave in pan)
9. cool throroughly.
10. loosen sides of cake from pan; remove cake
11. frost if desired
12. enjoy