Heat oven to 350F. Grease and flour 2 round pans. Beat flour, sugar, baking powder, salt, milk, shortening, and vanilla in large mixer bowl on low speed, scraping bowl occasionally, 2 minutes. Beat in egg whites on high speed, scraping bowl occasionally, 2 minutes. Pour into pans. Bake until wooden pick inserted in center comes out clean or until cake springs back when touched lightly in center. Cook 30 to 35 minutes, cool 10 minutes; remove from pans. Cool completely. Fill layers with lemon filling.

Lemon Filling: Mix sugar, cornstarch, and salt in saucepan. Stir in water gradually. Cook, stirring constantly until mixture thickens and boils. Boil and stir 1 minute. Remove from heat; add lemon peel and butter. Stir in lemon juice and food coloring; cool. If filling is too soft, refrigerate until set.

White Frosting: Mix sugar, corn syrup, and water in saucepan. Cover; heat to rolling boil over medium heat. Remove cover and boil rapidly to 242F on candy thermometer or until small amount of mixture dropped into very cold water forms a ball that holds its shape when pressed. As mixture boils, beat egg whites until stiff peaks form. Pour hot syrup very slowly in a thin stream into egg whites, beating constantly on medium speed. Add vanilla; beat on high speed until stiff peaks form.