Preheat the oven to 350℉. Butter and flour a 9-inch springform pan or cake pan.
In a large mixing bowl combine the whole milk, extra virgin olive oil, eggs, grapefruit zest, grapefruit juice, and vanilla extract.
Add the granulated sugar, baking powder, salt, and flour and combine. Do not overmix, a few lumps are fine.
Bake for 26-28 minutes or until the top has a nice rounded dome, it is lightly brown and a tooth pick inserted in the middle comes out clean.
Once the cake has cooled, you can dust it lightly with powdered sugar (optional).
Notes
Do Not Overmix: A few lumps are okay and will bake out in the oven. Overmixing can cause gluten development which leads to a dense and tough cake (something you want in your pizza crust, but not in your cake).
Checking for Doneness: A toothpick inserted in the middle should come out clean without any wet or moist crumbs. The top should also be a light golden brown with a nice domed shape.
Room Temperature Ingredients: For a lighter cake, ensure that the eggs and milk are at room temperature.