Gently boil the orange in a saucepan of water for 45 minutes.
Remove the pips from the orange, then place them it in the blender, skin and all. You may need to add a little water to get the right consistency.
Preheat the oven to 180°C fan / 200°C.
Grease a 8" inch round cake tin with butter. Cut a disc of greaseproof paper and use to line the tin
Beat together the eggs and sugar until light and pale.
Gently fold in the orange puree, add the ground almonds, baking powder and stir to combine
Pour the batter into the tin and bake for 30 minutes or until golden on the top.
Leave to cool in the tin before turning out and serving