Preheat oven to 325°. Lightly oil 9-inch springform pan; set aside.
Combine flour, cornstarch, baking soda and salt in small bowl; set aside.
Combine cocoa with granulated sugar in large bowl. Blend in water, then olive oil, egg, egg white and vanilla with wire whisk until smooth. Add flour mixture and whisk in just until smooth. Pour into prepared pan.
Bake 45 minutes or until toothpick inserted in center comes out clean Cool completely on wire rack. Loosen cake from sides of pan with small spatula or butter knife. Remove to serving plate, then sprinkle with confectioners sugar. Cut into small wedges to serve.