Preheat the oven to 325˚F. Spray a 9-inch cake pan (with at least 2-inch tall sides) with baking spray. Line the pan with a circle of parchment paper. (you can also use a 9-inch springform pan).
Combine the sugar and eggs in a medium-size bowl. Whisk well until light and fluffy (30-40 seconds).
Add the buttermilk, orange zest, orange juice, vanilla extract, baking powder and salt and whisk until everything is well combined.
Add the flour and whisk just until incorporated. It’s okay at this point if there are still some lumps.
Add the olive oil. At first, it will seem separated but then it will come together. Whisk until the olive oil is incorporated and the mixture is smooth (30-45 seconds).
Transfer to oven and and bake for 35-45 minutes until medium golden brown and internal temperature is 204-210˚F or a toothpick comes out clean when inserted in the center of the cake. Cover the cake loosely if it seems to be getting too brown before it’s done.
Cool in the pan for 10 minutes then invert onto a cooling rack that has been set on top of a piece of foil.
While the cake is cooling in the pan, make the glaze by combining the powdered sugar and orange juice and in a small bowl. Stir until smooth.
With a pastry brush, gently brush and pat the glaze all over the cake. Just keep going over the cake till the glaze is gone. Some of it will drip off, but most of it will soak in. Allow cake to cool. Sprinkle with powdered sugar if desired and serve.
See Café Tips above in the post for more detailed instructions and tips.