Adapted from Maialino's Olive Oil Cake. I substituted grapefruit for the orange and lemon zest, reduced the olive oil, subbed vanilla extract for the Grand Marnier, baked in a 10" instead of 9" pan, and added a grapefruit rosemary glaze. —Brittney
Preheat the oven to 350 F. Spray a 10" round cake pan (at least 2" deep) with cooking spray and line the bottom with parchment paper.
In a medium bowl, whisk all dry cake ingredients (through baking powder). In another bowl, whisk remaining ingredients. Add the dry ingredients to the wet and whisk until just combined.
Pour cake batter into prepared pan and bake on middle rack for about 45 minutes, or until a tester comes out clean and cake bounces back to touch. Set the cake on a rack to cool for about 30 minutes.
Invert the cake onto the rack to cool completely, making sure the sides have released from the pan first. Leave to cool 1-2 hours.
When cake is completely cool, prepare glaze by mixing all ingredients in a small bowl. Add more powdered sugar as needed. The glaze should still be thick enough to stick but thin enough to still spread itself on the cake.
Move the cake to a serving dish and pour the glaze over the top. Let sit for 30 minutes before serving so the glaze can be absorbed and set slightly. Goes great with vanilla ice cream!