Preheat oven to 180C. Grease loaf pan with butter and set aside.
Whisk together eggs and sugar on high speed until pale and fluffy, about 5 minutes. At low speed and with the mixer running, add oil slowly until combined. Add orange juice, zest, and vanilla extract and keep whisking slowly until combined. Add flour mixture and whisk just until combined. Don’t overmix.
Pour batter into the prepared pan. Bake for 40-50 minutes or until a toothpick inserted into the centre of the cake comes out clean. If the top is browning quickly while baking, cover loosely with aluminum foil. Allow cake to cool, decorate with icing sugar.