'This is hands-down one of my favorite recipes,' says the author of the Dana's Bakery cookbook, which is filled with desserts from her South Hackensack, N.J., shop. 'It's light, airy and perfect for summer!'
Preheat oven to 325°. Sift together flour, caster sugar, cornstarch and salt into a bowl; set aside.
Beat egg whites and granulated sugar with a stand mixer fitted with a whisk attachment on high speed until soft peaks form, 4 to 5 minutes. Add vanilla; beat until just combined, about 1 minute.
Using a rubber spatula, gradually fold sifted flour mixture into egg white mixture in about 3 additions.
Divide batter in thirds in different bowls (about 3 ½ cups each). Fold a few drops of red food coloring into batter in one bowl; fold a few drops of blue food coloring into batter in second bowl, and leave remaining batter undyed.
Spoon red batter evenly into an ungreased 10-inch tube pan. Spoon white (undyed) batter evenly over red batter; spoon blue batter evenly over white batter. Bake in preheated oven until a wooden pick inserted into center of cake comes out clean, 40 to 45 minutes. Remove from oven, and immediately flip cake upside down (do not remove cake from pan) onto a wire rack. Let cake cool in pan completely, about 2 hours.
Run a knife around edges of cake to loosen from pan, and remove cake from pan. Sprinkle cake with powdered sugar, slice and serve.