Preheat oven to 180°C (350°F) and grease a 9-inch springform cake tin. Line the bottom with parchment paper.

Zest the entire orange into a large bowl and set aside. Remove and discard the white pith from the orange, blend the flesh until smooth, and set aside.

Sift together flour, cornstarch, baking powder, and salt. Set aside.

In the bowl with the orange zest, add butter, oil, and sugar. Cream for 2 minutes until light and fluffy.

Add eggs one at a time while mixing on low speed, mixing well between additions.

Add the blended orange, milk, and vanilla. Mix on low speed until well combined.

Fold the pre-sifted dry ingredients into the wet ingredients until just combined. Be careful not to over-mix.

Pour the batter into the prepared cake pan, smooth out the top, then tap the pan on the counter to release large air bubbles. Bake for 35 minutes or until a toothpick comes out clean.

Cool the cake in the pan for 15 minutes, then run a knife around the edges, remove the outer ring, and let it cool to room temperature before dusting with powdered sugar.