Rub a 9-inch round cake pan with olive oil and fit a 9-inch circle of parchment paper into the bottom of the pan. Put the pan into the oven and heat the oven to 400ºF (200ºC).
Add the flour, sugar, baking soda and baking powder to a large mixing bowl and whisk until combined. In another medium mixing bowl whisk together the milk, olive oil, eggs, orange zest and orange juice until thoroughly combined. Stir the wet ingredients into the dry until just combined and no flour remains.
Pour the batter into the heated cake pan and turn the oven down to 350ºF. Bake until a knife inserted into the middle of the cake comes out clean, about 1 hour.
Let cool for 10 minutes then carefully run a knife around the side of the cake pan and turn the cake out onto a cooling rack. Let cool completely before topping.
For the dried winter citrus slices:
Heat the oven to 250ºF. Arrange the citrus slices on a silpat or parchment paper lined baking sheet.
Bake, flipping the slices every 15 minutes until the citrus slices are completely dried out but not browned, about 1 hour (depending on the size and thickness of the slices - some may finish sooner than others). Remove to a wire cooling rack and let cool completely.
Slices can be made and stored up to 3 weeks ahead of time.
For the whipped cream:
Add the heavy whipping cream, mascarpone and confectioners sugar to the bowl of a stand mixer. Begin whipping at medium speed until frothy and bubbly.
Turn the speed up to high and continue to beat until soft peaks form, about 7 minutes. Cover and refrigerate until ready to serve.
For assembly:
Use a rubber spatula to spread the whipped mascarpone cream over the top of the cake. Spread some around the sides so it is slightly covered but has the “naked” effect. Arrange the dried citrus over the top of the cake and serve.