|Egg whites||1 1⁄4 Cup (20 tbs) (About 9 Large Egg Whites)|
|Cream of tartar||1 1⁄2 Teaspoon|
|Vanilla extract||1 Teaspoon|
|Granulated sugar||1 1⁄2 Cup (24 tbs)|
|Cake flour||1 Cup (16 tbs) (Not Self Rising)|
|Egg yolks||4 Large|
|Sifted confectionery sugar||1 1⁄4 Cup (20 tbs)|
1. Preheat oven to 375°F. From oranges, grate 1 tablespoon plus 1/2 teaspoon peel and squeeze 1 tablespoon juice. From lemon, grate 2 teaspoons peel and squeeze 1 tablespoon juice. Reserve.
2. In large bowl, with mixer at high speed, beat egg whites, cream of tartar, vanilla, and salt until soft peaks form when beaters are lifted. Sprinkle in granulated sugar, 2 tablespoons at a time, beating until sugar has dissolved and egg whites stand in stiff, glossy peaks when beaters are lifted.
3. Reduce speed to low; gradually beat in flour just until mixture is blended.
4. In another large bowl, with mixer at high speed, beat egg yolks until thick and lemon-colored. With rubber spatula, fold in half of egg-white mixture, 1 tablespoon orange peel, and lemon peel just until blended.
5. In ungreased 10-inch tube pan, alternately drop 1/2 cups of white and yellow batters. Run narrow metal spatula through batter for marbled effect. Bake until cake springs back when lightly pressed, 35 to 40 minutes. Invert cake in pan onto large metal funnel or bottle; cool completely in pan. Run thin knife around cake to loosen from side and center tube of pan. Remove from pan and place on cake plate.
6. Prepare orange-lemon glaze: In small bowl, combine confectioners' sugar, reserved orange and lemon juices, and remaining 1/2 teaspoon orange peel to make a smooth glaze; spoon over cooled cake.