White Batter: In a medium bowl, sift flour and ½ cup sugar.
In a large bowl, with an electric mixer, beat egg whites, salt and cream of tartar until soft peaks form when beaters are raised. Beat in 1 cup sugar, a little at a time, beating well after each addition un til stiff peaks are formed. With a wire whisk, fold in lemon extract until combined. Fold the flour mixture a ¼ at a time, with a wire whisk, rotating bowl after each addition. Turn 1/3 of batter into a medium bowl.
Preheat oven to 375º.
Yellow Batter: In a medium bowl, combine egg yolks, 2 tablespoons flour, and 2 tablespoons sugar, and mix with an electric beater until very thick.
Fold the egg mixture into the reserved one third batter, to gently combine.
Spoon batters, alternately, into an ungreased 10” tube pan to marble. Ending with white batter on top. With knife, run thru batter 2 times to complete marbling. Make sure batter is spread evenly on top and touches side of pan.
Bake on lower rack of oven, 35-40 min, or until cake springs back when pressed with fingertip. Invert pan and let cool for 2 hours.
Loosen cake from pan , place upright on a serving plate and dust with confectioners sugar before serving.