Preheat your oven to 350°F (180°C). Grease and line a 7-inch (18 cm) cake pan with parchment paper.
Wash the orange well, (ideally is best to use an organic orange) remove the top and bottom ends (where the zest is thick), and cut into chunks. Leave the peel on.
Add the chopped orange, sugar, oil, milk, eggs, and vanilla to your blender.
Blend until smooth and creamy.
Sift in the flour and baking powder, then pulse briefly at the lowest speed and continue with a spatula. Do not overblend.
Pour the batter into a butter and floured pan or a parchment paper lined pan.
Bake for about 45 minutes, or until a toothpick inserted in the center comes out clean to ensure it's cooked thoroughly
Let cool in the pan for 10 minutes, than remove it from it. Dust with icing sugar, slice, and serve!