Preheat oven to 350 degree F. Grease and flour two 9x1-1/2-inch round cake pans; set aside. Finely shred 1 tablespoon of peel from 1 orange. Squeeze juice from 2 oranges to measure 1/2 cup juice. Section remaining orange. In a large mixing bowl beat egg whites to soft peaks. Gradually add 1/2 cup of the sugar, beating to stiff peaks. In another large mixing bowl combine flour, baking powder, salt, and remaining 1 cup sugar.
Add milk and oil. Beat on low speed of electric mixer until combined. Add orange juice and egg yolks; beat 1 minute. Gently fold in egg white mixture until combined. Fold in orange peel. Divide batter evenly between pans. Bake for 30 to 35 minutes or until a wooden toothpick inserted near the centers comes out clean. Cool completely on wire racks; remove from pans. Frost with Orange Fluff Frosting. Top with reserved orange sections. Makes 12 servings.
Orange Fluff Frosting
In a small saucepan stir together sugar and cornstarch. Stir in orange juice. Cook and stir over medium-low heat until mixture is thickened. Cook and stir for 2 minutes more. Remove from heat; stir in orange peel. Cover and chill for 1 hour. In a large bowl beat cream with an electric mixer on medium to high speed until stiff peaks form (tips stand straight). Gently fold in orange juice mixture.