Cover oranges with water and bring to boil in lidded saucepan for 1.5 hrs until soft.
Remove water and allow oranges to cool down. Halve them to remove pips. Puree the oranges including the rind with a (hand) blender.
Mix eggs and sugar in a bowl, followed by backing powder and tropical almond flour. Add pureed oranges to the batter. Since the batter is flourless, you can expect it to be quite runny.
Preheat oven to 190°C. Pour batter into a greased and floured 22-24 cm springform tin. Bake for about 45 min - 1 hr.