Preheat your oven to 180 Celsius/ 350 Fahrenheit.
Line a rectangular bread baking tin with baking paper or use a well-greased silicone baking tin.
Put the oranges into a pot filled with cold water and cover with a lid. Bring to the boil, then simmer for at least 1 hour. Make sure the oranges are always submerged. This removes the bitterness.
Drain the water and let the oranges cool down.
Cut the oranges in half and remove any seeds, then puree in a food processor or with a stick blender.
Separate the eggs and whisk the egg whites until stiff peaks form. This will make the cake lighter in texture. I did it by hand - it's easier than you think. Just use a clean, dry metal bowl, an old-fashioned whisk plus a bit if perseverance.
Add all ingredients except the egg whites to the orange pulp and mix. Lastly, fold in the egg whites until well-combined.
Make sure you test your batter for sweetness and adjust to taste.
Pour the batter into your cake tin and sprinkle flaked almonds on top.
Bake for 50 minutes or until a knife inserted comes out clean.