Preheat the oven to 350~. Grease and flour 2 (8") round cake pans or a 9x13" pan. Combine the flour, cornstarch, salt and baking powder, and sift them twice. Put the butter in a large mixing bowl, and beat until it is smooth and creamy. Gradually add 1 cup of the sugar, and beat until the mixture is well blended. In a separate mixing bowl, beat the egg whites until they begin to foam. Then gradually addd the remaining 1/2 cup sugar, and continue beating until the whites are stiff, but moist; set aside. In a separate mixing bowl, beat the egg yolks to break them up, then add the orange juice and orange zest, and continue to beat until the mixture is pale and thick. Add the egg yolks to the butter/sugar mixture, and mix gently until blended...it will look slightly curdled. Sift the flour mixture over, and fold in. Scoop up the beaten egg whites, drop them on top of the batter, and gently fold them in until there are no streaks of unblended white. Pour into prepared pan or pans, and smooth the top with a rubber spatula. Bake for 20-30 minutes, or until pick inserted in the center comes out clean. Remove from oven, and let cool for about 5 minutes before turning the layers out. The 9x13" cake should be left in the pan to cool slightly before adding the Glaze. Orange Glaze: Mix powdered sugar with orange juice and grated orange zest until smooth. Drizzle over warm cake.