Wash your clementine and then cut into quarters. Blitz in a food processor or blender (see note 2).
Preheat the oven to 175℃ / 350℉. Line and/or grease a 6” / 18cm springform pan.
Beat the sugar and butter together until light and fluffy.
Add one egg at a time, making sure it is fully incorporated before adding the next.
Combine the flour, almonds, polenta, and baking powder in a separate bowl. Add the dry ingredients a little at a time.
Finally, add your clementine (there should be about 2 tablespoons once it has been blitzed).
Dollop the batter into your prepared pan and bake in the lower part of the oven for 35-45 minutes. It is ready when a skewer inserted comes out clean.
Remove from the oven and allow to sit for ten minutes before removing the outer edge of the springform.
Place on a wire rack and allow to cool completely.
When ready to serve, sprinkle a little icing / powdered sugar over the top of the cake.
Serve with a dollop of mascarpone and some fresh fruit (if you like).