Beat egg yolks until thick and lemon-colored. Add peel and juice. Beat until very thick. Gradually beat in 1 cup of sugar and the salt. Carefully fold in flour. Beat egg whites until foamy; add cream of tartar; beat until soft peaks form. Thoroughly fold whites into yolk mixture. Bake in ungreased 10-inch tube pan at 325 deg. About 55 minutes or until done. Invert pan; cool and frost.
Cream butter; gradually add about half the sugar, blending well. Beat in vanilla. Gradually beat in remaining sugar. Add enough orange juice to make of spreading consistency.
