Orange and pistachio polenta cake

Preheat oven to 180C, and grease and line a 23cm tin. Beat the butter and castor sugar until light and fluffy. Beat in the eggs one at a time. Fold in the pistachios and polenta. Grate the zest of 2 of the oranges and fold into the mixture along with the baking powder. If the mixture is very thick add the juice of one orange. Pour the mixture into your prepared tin and bake for 45 minutes to 1 hour (until a skewer comes away clean). Remove the cake from the oven and set aside to cool.
In a pot mix together the remaining juice of the oranges, and about 4 tbsp of sugar to taste. Bring this sauce to the boil and remove from the heat. Pour the sauce over the cake (pricking little holes in the cake to help it absorb all the sauce). Leave to cool and serve with creme fraiche or yoghurt.