Sift cake flour once, measure, add baking powder, salt, then sift together 3 times.
Cream butter, add sugar gradually; Creaming together until light and fluffy.
Add flour mixture, alternately with milk, a small amount at a time; Beat after each addition until smooth.
Add vanilla, then fold in egg whites.
Bake in 3, nine inch layer pans in preheated slow oven 325ºF for 15 minutes, then increase heat slightly to 350ºF and bake 15 minutes longer or until toothpick inserted in center comes out clean.
Cool cake completely on wire racks.
Prepare Lemon pudding (Cooked not instant): In a medium size sauce pan mix contents of pudding box with 1/2 cup sugar and 1/4 cup water.
Stir in 2 egg yolks and an additional 2 cups water; Cook over medium heat, stirring constantly until mixture comes to a full bubbling boil.
Remove from heat and cool 5 minutes stirring twice then cool to room temperature.
Fill cake with Lemon pudding between the layers and frost with Moon Glow Lemon Frosting.
To make Moon Glow Lemon Frosting: Add lemon rind and juice to yolks; Mix and add sugar; Beat until smooth.
Note: For those afraid of eating raw egg you can do this to make the egg yolks safe: In a heavy saucepan, stir together the egg yolks and liquid from the recipe (at least 2 tablespoons liquid per yolk); cook over very low heat, stirring constantly, until the yolk mixture coats a metal spoon with a thin film, bubbles at the edges or reaches 160 degrees F, as measured with an instant read thermometer. Immediately place the saucepan in ice water and stir until the yolk mixture is cool; proceed with the recipe.