How to Make It
Beat butter at medium speed with an electric mixer about 2 minutes or until creamy. Gradually add sugar, beating 5 to 7 minutes.
Beat egg yolks lightly; add to butter mixture, beating until well blended.
Combine flour, baking powder, and salt; add to butter mixture alternately with orange juice and water, beginning and ending with flour mixture. Beat at low speed with an electric mixer until blended after each addition. Stir in vanilla.
Beat egg whites at high speed with an electric mixer until foamy; reduce speed to medium, and beat until stiff peaks form. Fold egg white into batter; spoon batter into a greased and floured 12-cup Bundt pan or 10-inch tube pan.
Bake at 350° for 45 to 50 minutes or until a wooden pick inserted in center comes out clean. Immediately place pan on a double layer of damp cloth towels; press towels around sides of pan, and let stand 10 to 15 minutes. Remove cake from pan, and cool completely on a wire rack.
Prepare the Orange Glaze: Squeeze juice from oranges; pour through a wire-mesh strainer into a 1-cup liquid measuring cup, straining out any seeds. Measure 1 cup juice; reserve remaining orange juice for another use. Combine sugar and cornstarch in a small saucepan; add lemon juice and 1 cup orange juices, stirring well with a wire whisk. Cook over low heat, stirring until sugar dissolves (about 10 minutes). Stir about one-fourth of hot mixture into yolks; add to remaining hot mixture, stirring constantly. Cook over low heat, stirring constantly, 10 minutes or until thickened. Remove from heat; add butter, stirring until well blended. Cool; cover and chill.
Prepare the Candied Orange Zest: Remove zest (orange part only) from oranges, using a zester, being careful not to remove white pith. Cut zest into 2-inch strips. Combine water and sugar in a small saucepan; cook over medium heat until boiling. Reduce heat to low; stir in zest, and cook mixture 15 to 20 minutes or until candy thermometer registers 220°. Remove zest strips from syrup with a slotted spoon, and spread on wax paper to cool. Sprinkle with additional sugar, if desired.
Spoon Orange Glaze over cake; top with Candied Orange Zest.