Preheat the oven to 175 degrees Celsius.
Line a 20 cm spring form with parchment paper
Add milk, olive oil, vanilla extract and sugar to a bowl and mix until combined and smooth.
Add orange zest and juice and mix again.
Combine polenta, oat flour, saffron, baking soda and salt in a separate bowl and combine. Then add to the wet ingredients and mix until you have a smooth batter. Let the batter rest while you prepare the orange.
Cut off the peel and white pith from the orange with a paring knife, then slice them into even rings, removing any seeds. Arrange the oranges at the bottom of the spring form.
Pour the batter over the arranged oranges and place in the middle of the oven and bake for 30-35 minutes. The cake is done when the edges have set and a toothpick comes out clean. The cake is ready when the edges are set but the middle might still look a little wobbly. It will set while it cools. So don't bake the cake for too long, but make sure a toothpick comes out clean.
Remove from the oven and let the cake cool completely before removing it from the spring form.
When the cake has cooled run a knife around the edges to loosen the cake. Remove the spring form, place a plate over the polenta cake and flip upside down so you have the oranges facing up.