Wash And Dry The Lemons And Oranges.
Grate The Lemons To Yield 1 Tablespoon Zest.
Reserve Lemons For Another Use.
Grate The Oranges To Yield 3 Tablespoons Zest.
Cut The Oranges In Half And Juice To Yield ¾ Cup.
Set Zests And Juice Aside.
Place A Rack In The Center Of The Oven, And Preheat The Oven To 325°F.
Set Aside An Ungreased 10″ Tube Pan.
Place The Flour, Sugar, Baking Powder, And Salt In A Large Mixing Bowl, And Stir To Combine.
Make A Well In The Middle Of The Dry Ingredients.
Add In The Following Order, Without Mixing, The Oil, Egg Yolks (Reserve The Whites), The Lemon And Orange Zest, And The Orange Juice.
With A Strong Wire Whisk, Beat Until Smooth, About 1 Minute.
Set Aside.
In A Large Mixing Bowl, Beat The Egg Whites And Cream Of Tartar With An Electric Mixer On High Speed Until A Stiff Peak Holds When The Beater Is Raised, 3 To 4 Minutes.
In 3 Additions, Fold About Three-Quarters Of The Yolk Mixture Into The Whites.
Next Fold The Whites Into The Remaining Yolk Mixture.
Gently Pour The Batter Into The Prepared Pan.
Bake For 55 Minutes At 325°F.
Then Increase The Temperature To 350°F And Bake For An Additional 8 To 10 Minutes.
Remove The Cake From The Oven, And Immediately Hang The Pan Upside Down Over The Neck Of A Bottle Or A Funnel, So That It Is Cooling Upside Down For 1 Hour.
With A Sharp Knife, Trim The Cake Away From The Edges Of The Pan.
Give The Pan A Gentle Shake, And Invert The Cake Once And Then Again Onto A Serving Plate.
If Desired, Drizzle With Orange Glaze.
Orange Glaze: Place 1 Cup Confectioners’ Sugar In A Small Bowl And Whisk In 2 Tablespoons Orange Juice.
When Smooth, Spoon The Glaze Over The Top Of The Cooled Cake.
If Desired, Sprinkle A Little Confectioners’ Sugar On Top.
