Preheat oven to 350° F. Lightly grease and flour a round 10-inch springform baking pan.
Sift together the flour, baking powder, baking soda, salt, cinnamon, and cocoa two times. In a large separate bowl, combine the sugar, oil, and orange zest, mixing well. Add the whole egg and egg whites, one at a time, mixing well after each addition. Stir in the zucchini. Combine the buttermilk and vanilla in a separate cup.
Add the dry ingredients to the zucchini mixture alternating with the buttermilk and vanilla, a third at a time, mixing well after each addition. Stir in the chocolate chips until just combined. Pour into prepared pan and bake 30 to 35 minutes, or until a wooden pick inserted in center comes out clean.
Let the cake cool on a wire rack for about 20 minutes, then run a knife around the edge of the springform pan, between the pan and the cake. Remove the sides of the pan. When the cake is completely cool, sprinkle with confectioners' sugar.
Serves 8 to 10
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