6 egg whites (3/4 cup)
1 3/4 cups sifted all purpose flour
1/4 tsp salt
1 1/2 cups sugar
6 egg yolks
6 Tbsp fresh orange juice
1 Tbsp freshly grated orange peel
1. In large bowl of electric mixer, let egg whites warm to room temperature-about 1 hour. Measure flour; sift about 2 cups flour once on a sheet of waxed paper; fill cups lightly to overflowing; with spatula cut off excess to make 1 3/4 level cups. Sift flour with salt; set aside.
2. With electric mixer at medium speed, beat egg whites until foamy. Gradually beat in 1/2 cup sugar, 2 Tbsp at a time, beating well after each addition. Continue beating until stiff peaks form when beaters are slowly raised. Set aside. Preheat oven to 350 degrees.
3. In small bowl of electric mixer, with the same beaters at high speed, beat egg yolks until very thick and lemon-colored-about 3 minutes. DO NOT UNDERBEAT. Gradually beat in remaining 1 cup sugar; continue beating until mixture is smooth.
4. At low speed, blend flour mixture and orange juice alternately into egg-yolk mixture, beginning and ending with flour and guiding batter into beaters with scraper. Add orange peel. Wish a whisk or rubber spatula, using under-and-over motion, fold yolk mixture gently into whites.
5. Pour batter into an ungreased 9 3/4-to-10-by4 1/2-inch kugelhopf pan (large bundt pan) or 10-by-4 1/2-inch tube pan without a removable bottom. Bake 50 to 55 minutes in kugelhofp or 35 to 40 minutes in tube pan, until cake springs back when pressed with finger. Invert over bottle; cool completely.
6. Using an up-and-down motion, run spatula around edge of cake and tube. Invert cake and shake to release; place on serving plate. Sift powdered sugar over top of cake.