Place the blood orange in a saucepan and cover with water. Bring to the boil and then simmer for 1 hour.
Pre-heat the oven to 180°C and line and grease a 20cm round cake tin.
Remove the oranges from the saucepan and cut in half to remove and discard the pips.
Place the oranges in a blender and blitz until smooth.
Beat the eggs and sugar until pale and thick.
Mix in the pureed orange.
Add the polenta, ground almonds, baking powder and rosemary leaves. Mix until thoroughly incorporated.
Pour the batter in the prepared cake tin and bake for around 40-45 mins until firm to the touch and an inserted toothpick comes out clean.
Once the cake is ready, remove from the oven and prepare the honey syrup by dissolving the honey in 2 tbsp blood orange juice in a saucepan on medium heat. Once dissolved and reduced slightly, prick the cake all over with a toothpick and pour the honey syrup all over the surface of the cake.
Let the cake cool in the cake tin before removing and serving.