Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.
In a large bowl, whisk together the sugar, eggs, olive oil, buttermilk, lemon juice, lemon zest, and rosemary.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Pour the batter into the prepared cake pan and spread evenly.
Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean.
Let the cake cool in the pan for 10 minutes before inverting it onto a wire rack to cool completely.
Once cooled, dust with powdered sugar, if desired.