WHITE BATTER...remove eggs from fridge and leave on counter for at least an hour..while waiting for the eggs to get to room temperature sift the 1 1/4 cups flour with 1/2 cup sugar 3 times.
With Electric mixer at high speed beat egg whites with cream of tartar until soft peaks form when beater is slowly lifted..beat in sugar 1/4 cup at a time until stiff peaks form when beater is slowly lifted.. with wire whisk fold vanilla into egg whites until combined sift flour mixture one fourth at a time over egg whites with wire whisk using an over and under motion gently fold in after addition with 15 strokes fold 10 more strokes to completely blend put 1/3 batter into medium bowl Preheat oven to 375F. .
Make yellow batter....In separate bowl co,bine yolks.cake flour and sugar..with mixer at high speed beat until very thick add lemon zest..with wire whisk fold with over and under motion yolk mixter into reserved 1/3 batter using about 15 to 20 strokes.
For marbling spoon batters alternately into 10 inch ungreased tube pan ending with white batter on top..bake on lower rack 35 to 40 minutes or until cake springs back when lightly pressed with fingertip..invert over neck of wine bottle or bottle on hand and cool for 2 hours..run a table knife around edge of cake to remove from pan sprinkle with confectioners sugar...cut with sawing motion with serrated knife.