.Preheat over to 325. Sift flour with 1/2 cup of the sugar. Repeat sifting 3 times; set aside. Beat egg whites in bowl of electric mix until frothy. Beat in cream of tarter. Add remaining 3/4 cup sugar gradually; beat until stiff peaks form. Sift flour and sugar mixture again over egg whites; fold in gently. Set aside.
Beat egg yolks, vanilla, orange juice and lemon juice in medium bowl until thick and pale yellow. Fold egg yolk mixture, orange rind and lemon rind into egg white mixture. Scrape batter into ungreased 10 inch tube pan.
Bake until top springs back when lightly pressed and a toothpick inserted in center comes out clean, about 1 hour and 10 minutes.
Let cool upside down 1 1/2 hours, setting tube over a bottleneck. Slide knife around cake to detach from pan, pressing knife against pan to avoid tearing cake.
For glaze, whisk together all glaze ingredients until smooth. Drizzle over cake allowing excess to drip down sides.