Preheat oven to 350°. Butter and flour a 12-inch cake pan.

In a large bowl, whisk together the eggs and granulated sugar until blended. Add the olive oil, milk and orange zest and mix well. In another bowl, stir together the flour, baking powder, baking soda, and salt. Add to the egg mixture, stirring just until blended. Do not overmix. Pour the batter into the prepared pan.

Bake until a toothpick inserted into the center comes out clean, 50-55 minutes. Remove to a wire rack to cool completely. Loosen the sides with a knife and invert onto a serving plate.

Dust the cake with confectioners' sugar and cut into 12 slices. Garnish the individual servings with fresh orange slices.