Wash the oranges and lemon, thoroughly scrubbing the peels.

Cut off the ends of the oranges. Cut the oranges in half, then cut each half into 4, so you're left with 8 pieces of orange. Discard any seeds.

Place the orange pieces in a food processor and pulse/chop until the rind is in very small pieces. Place a plate in the freezer, to help us test for doneness later.

Add oranges to a large saucepan over medium heat. Zest the lemon into the pot and squeeze the juice from it, into the pot. Add water and the sugar and stir well.

Bring mixture to a boil. Reduce heat to a low boil and simmer, stirring often, for 30-35 minutes until thickened. When done, it will slide off the spoon in sheets, not droplets, and a spoonful poured onto a cold plate should be a soft gel consistency that moves slightly. If after pouring onto a cold plate it's thin and runs easily on the plate, it is not ready, so continue cooking.

Pour into jars or containers with a lid. Allow to cool to room temperature, then store in the refrigerator for up to 2 weeks, or freeze for up to 3 months.