- Preheat oven to 325 °F.
- Line the bottom of a 9" tube pan with a doughnut shaped piece of wax paper, notching around the center circle every inch.
- Do not grease pan.
- Sift first 4 ingredients into a bowl.
- Set aside.
- Separate eggs, dropping 4 yolks into one mixing machine bowl and 10 whites into another.
- Using whisk attachment, beat egg whites on medium high speed until foamy.
- Turn speed up to high.
- Sprinkle in half the sugar and beat until stiff and glossy.
- Set bowl with yolks on machine.
- Beat until light.
- Sprinkle in remaining sugar, zests and concentrate.
- Beat on high speed until well blended.
- Using a wooden spoon, stir about ½ cup of beaten whites into yolks.
- Then pour all of yolk mixture over beaten egg whites.
- Fold in by hand in 12 sweeping strokes.
- Sift dry ingredients again over all and continue folding for another 12 strokes.
- Sprinkle and fold in nuts (another 12 strokes would suffice).
- Spoon into prepared pan, smoothing out top.
- Run a blunt knife around sides to dispel any air bubbles.
- Bake in center section of oven for 55 minutes. Top should be lightly browned and toothpick, when inserted, should come out clean.
- Remove from oven and invert tube onto a 3-cup mason jar with a 1½" neck, or any convenient holder that will fit the tube.
- Cool for 1½ hrs.
- Gently unmold.
- Peel off wax paper.
- When completely cooled, sift confectioner's sugar over.
- Cut with sharp serrated knife, or pull apart servings with fork.