Method

1. Use a vegetable peeler to remove a thin layer of the orange rind off the oranges. Cut the rind into matchstick size pieces.
2. Remove the thick white part from the oranges and discard. Cut the oranges into slices, discard any thick white stem parts and set aside.
3. Fill a medium saucepan with 2 cups of water and bring to a boil over high heat. Once boiling, add the orange rind and continue boiling over medium high heat for 10 minutes. Drain the water from the saucepan, then fill the saucepan with another 2 cups of water (keeping the orange rind in the saucepan). Place the saucepan over the stove over high heat for 10 minutes. One last time, drain the water from the saucepan and then fill with 2 more cups of water and place over high heat for 10 minutes.
4. Drain the water from the saucepan and add the orange slices, sugar,lemon juice, and 2 cups of water. Bring the mixture to a boil over high heat. After about 6 minutes, the contents of the pot should be boiling. Reduce the heat to medium-low so that the mixture is simmering.
5. Cook the marmalade for 40 more minutes, giving it a stir every 3 to 5 minutes to keep the contents from overflowing in the saucepan. After 40 minutes, the marmalade should look a lot thicker, although it still won't be as thick as it will be once it cools.
6. Stir in the cinnamon, then pour into a clean jam jar and let it rest on the counter until room temperature. Place the lid on top and chill in the fridge - it will firm up more as it cools.