Preheat oven to 350°F. Butter and line one large or two small cake pans. Separate egg whites from yolks. Beat egg yolks and 1/3 cup sugar until pale and thick. Add oil or melted butter, juices and zest. Whisk together 1/3 cup sugar and flours, then fold into the batter. Beat egg whites and salt until foamy, then gradually add remaining sugar and beat until stiff. Fold into batter. Bake 30min.