Preheat the oven 160c or gas mark 3. Grease a 22cm springform cake tin and line with baking parchment.
Place 2 oranges in a pan, cover with cold water and turn up to a medium heat. Leave them to simmer for an hour until they have softened. Drain the oranges and slice them in half, remove the seeds, scoop out the flesh. Add the flesh and orange skin to a food processor and blitzed to a soft puree.
Zest the remaining orange and ruby grapefruit, leave these delicious zesty shavings to one side.
Grab the zested orange and both grapefruits ruby and pink, use a knife to remove the top and base from each then cut and peel the pith from both sides. Slice out the segments. Save the remaining parts for juice later.
Arrange the orange and grapefruit segments at the base of the tin.
Beat the egg yolks with the honey until thick and pale. Mix together the polenta, almonds, salt and baking powder then fold the egg and honey mixture followed by the oil, pureed orange mixture and the orange and grapefruit zest.
In a separate bowl whisk the egg whites until they form stiff peaks then fold them into the tasty cake batter.
Bake this delicious cake in the centre of the oven for 75-90 minutes. Insert a skewer into the cake, when it comes out clean the cake is done.
While the cake is gently baking away you can make the syrup. Combine the citrus juices and honey in a pan, stir well and bring to a boil. Leave it to simmer for roughly 5 minutes.
Once the cake is baked to perfection, remove it from the oven and leave it to cool on a cooling rack. Remove the cake from the tin, flipping it so the base is on the top with the lovely now caramelised segments. Drizzle warm sticky syrup over the top of the cake and serve immediately to your loving hungry for cake guests....Delicious with a scoop of ice cream or creamy creme fraiche....