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1
Preheat oven to 350F.
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2
Butter and flour pan, knocking out excess flour.
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3
Into a large bowl sift together flour, 1/2 cup granulated sugar, baking powder, and salt.
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4
Separate eggs.
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5
In a small bowl whisk together yolks, oil, orange juice, zests, and vanilla and whisk mixture into flour mixture until batter is smooth.
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6
In another large bowl with an electric mixer beat whites with cream of tartar until they just hold soft peaks.
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7
With mixer on low speed gradually add remaining 1/4 cup granulated sugar and beat until whites hold stiff, glossy peaks.
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8
Stir about one third whites into batter to lighten and fold in remaining whites gently but thoroughly.
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9
Spoon batter into pan (batter will reach top of pan).
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10
Bake cake in middle of oven until golden and a tester comes out clean, about 40 minutes.
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11
Immediately invert pan onto a rack and cool cake completely in pan upside down on rack.
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12
Run a thin knife around outer edge of pan and turn cake out of pan onto a serving plate.
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13
Cake may be made 2 days ahead and kept in an airtight container at cool room temperature.
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14
Sprinkle cake with confectioners' sugar and serve, sliced, with syrup.
