Score around the outside of the oranges in quarters, and gently using your fingers take off each quarter of the peel.
Bring a pan of water to the boil then add the orange peel and boil for two minutes.
Drain the peel and discard the water.
Refresh the peel in cold water, and then repeat the blanching process twice more.
Put the 500ml of water, sugar and vanilla in a saucepan and bring to the boil.
Add the drained orange peel and bring back to a boil, then reduce to a low heat and continue to cook for around 2 hours, until the orange is soft and candied.
Store in an airtight container along with it's syrup for up to 1 month.