Preheat your oven to 350°F (175°C).
In a mixing bowl, combine the baking powder, kosher salt, and all-purpose flour.
In another bowl, whisk together the sugar, olive oil, orange zest, vanilla extract, and the brown egg until well blended.
Gradually add the dry ingredients to the wet mixture, alternating with the milk, and mix until smooth.
Pour the batter into a prepared cake pan and spread it evenly.
Bake in the preheated oven for about 30-35 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cake to cool slightly before inverting it onto a serving plate.
