Preheat oven to 160ºC . Line the bottom of a 23 cm tube pan with a doughnut shaped piece of wax paper, notching around the cun center circle every inch. Do not grease pan. Sift first 4 ingreds. into a bowl. Set aside. Separate eggs, droping 4 yolks into one mixing machine bowl and 10 whites into another. Using whisk attachment, beat egg whites on med.hi 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 abt. a half c. of beaten whites into yolks. Then pour all of yolk mixture over beaten egg whites. Fold in by hand in dozen sweeping strokes. Sift dry ingreds. again over all and continue folding for another dozen strokes. Sprinkle and fold in nuts (another dozen 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 min. 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 4 cm neck, or any convenient holder that will fit the tube. Cool for 1.5 hrs.. Gently unmold. Peel off wax paper. When completely cooled, fift confectioner's sugar over. Cut with sharp serrated knife, or pull apart servings with fork. Frances Prince's New Jewish Cuisine