WHITE BATTER:

1 3/4 c. egg whites (12 to 14)
1 1/4 c. sifted cake flour, sift before measuring
1 1/2 c. sugar
1/2 tsp. salt
1 1/2 tsp. cream of tartar
1 1/2 tsp. vanilla extract

YELLOW BATTER:

5 egg yolks
2 tbsp. cake flour
2 tbsp. sugar
2 tbsp. grated lemon peel
Confectioners' sugar

Make white batter: In large bowl, let whites warm to room temperature 1 hour. Sift 1 1/4 cups flour with 1/2 cup sugar; re-sift 3 times. With electric mixer at high speed, beat whites with salt and cream of tartar until soft peaks form when beater is slowly raised.

Beat in 1 cup sugar, 1/4 cup at a time, beating well after each addition. Beat until stiff peaks form when beater is slowly raised. With wire whisk, fold vanilla into egg whites until combined. Sift flour mixture, 1/4 at a time, over egg whites.

With wire whisk, using an under-and-over motion, gently fold in each addition with 15 strokes, rotating bowl 1/4 turn after each addition. Fold 10 more strokes, to blend completely. Turn 1/3 batter into medium bowl. Preheat oven to 375 degrees.

Make yellow batter: In small bowl, combine yolks, cake flour and sugar. With mixer at high speed, beat until very thick. Add lemon peel. With wire whisk, using an under-and-over motion, fold yolk mixture into reserved 1/3 batter with 15 strokes.

For marbling, spoon batters alternately into an ungreased 10-inch tube pan, ending with white batter on top. With knife, cut through batter twice. With rubber scraper, gently spread batter in pan until it is smooth on top and touches side of pan all around.

Bake on lower oven rack 35 to 40 minutes, or until cake springs back when pressed with fingertip. Invert pan over neck of bottle to cool 2 hours. With spatula, loosen cake from pan; remove. Sprinkle with confectioners' sugar, if desired. Serves 10.

NOTE: To get good volume, let egg whites warm to room temperature before beating them. Be sure to use cake (not all-purpose) flour in this recipe. If you are baking the cake a day ahead, leave it in the pan overnight and remove it just before serving. Cut cake with a knife with a serrated edge, using a light, sawing motion. Nice served with ice cream.