Rinse the oranges under running water. Cut them in a half and squeeze the juice, then collect it in a jar. Remove any white skin remained inside the oranges and cut the zest into thin strips. Put the zests in a large bowl and pur in the orange juice. I got 500 ml of juice and 700 g of zests. Add 2 liters of water and let stand overnight.

The next day, pour the entire content of the bowl into a large pot and bring to the boil. Let it simmer gently covered on low flame for about 1 hour and a half, until the zests become soft.

Add the lemon juice and the sugar and stir with a wooden spoon to melt. Bring it back to the boil and let it simmer gently for at least forty minutes. Check if it is ready: pour a drop of marmalade on a cold saucer from the fridge. If it solidifies and does not slip away when you tilt the saucer, it is ready to be put into sterilized jars.