Beat yolks until light yellow. Add sugar and beat well. Mix cake meal and potato starch in a small bowl and add alternately with juices and rind. Beat egg whites until stiff and fold into batter.
Pour into tube pan. Bake at 325F for 1 hour. Invert and cool completely before removing from pan.
Recipe by Opsreys Journeys at https://www.ospreysjourneys.com/?p=2878