Preheat oven to 350F. Butter and flour 9" springform pan with 2 3/4"-high sides. Finely grind almonds and flour in processor.

Beat 3/4 c powdered sugar and yolks in large bowl of electric mixer until thick and pale yellow, about 3 minutes. Mix in grated orange peel, then almond-flour mixture.

Beat egg whites (with clean dry beaters) and salt until beginning to form soft peaks. Gradually add remaining 1 c powdered sugar and beat until stiff but not dry. Fold whites into yolk mixture in 2 additions. Transfer batter to prepared pan. Bake cake until top is golden brown and tester inserted into center comes out clean, about 40 minutes. Cool cake in pan on rack.

(Can be made 1 day ahead. Cover and let stand at room temperature.)

Using small knife, cut around pan sides to loosen. Release pan sides. Serve with Orange-Cinnamon Syrup.

Syrup: Stir all ingredients in large saucepan over medium-low heat, until sugar dissolves. Increase heat and boil until syrup is reduced to 1 1/3 cups, about 12 minutes. Cool syrup. Discard cinnamon. (Can be made 2 days ahead. Cover and refrigerate)