Place oranges (whole) in a saucepan and cover with water. Bring to boil and simmer with lid on for 45 minutes. Drain and cool, reserving some of the liquid (½ cup is plenty). Roughly cut up the cooled oranges and place in a blender and puree until smooth and thick, adding only as much of the reserved liquid as needed (you may not need any but I find I always do, or it won't puree properly) - keep the puree as dry as possible. Beat eggs with sugar until thick, then add the orange puree, ground almonds and baking powder.

Pour mixture into a 23 cm tin that has been lined with baking paper (I actually just use a deep spring form tin about 23 cm diameter, cover the base with foil and lightly grease the foil base and sides of the tin). Bake in a moderate oven at 350° for 1 hour. Leave to cool in the tin before turning out (run knife around inside of tin to loosen first). The cake will be very moist and light. Sift icing sugar onto top of cake, decorate with orange zest if desired. Serve with plenty of cream.