To sterilize the jams jars, place them in a large saucepan and cover with cold water.
Bring the water to a boil and simmer for about 10-15 minutes.
Remove from the water with tongs - be careful not to burn.
Place them upside down on a clean surface to dry out while you are making the marmalade.
Begin with the marmalade by cutting the oranges in half.
Use a metal spoon and scoop out the flesh and collect the juice.
Leave the pith behind.
Reserve the shells.
Put the flesh, pips and juice in a food processor and blend it until smooth.
Push the puree through a sieve into a large saucepan.
Clean the shells of the oranges by scooping out as much of the pith as possible - the shells must be clean to cut the rind.
Slice the rind into very, very thin matchstick strips and add these to the sieved flesh in the saucepan.
Pour the lemon juice and water into the saucepan and bring this to a boil.
Reduce the heat and simmer for 1-1½ hours until the rind is very soft and the mixture is reduced by half.
Over a low heat, add the sugar and stir until it has dissolved.
Boil for about 10 minutes and skim off any froth from the surface with a slotted spoon.
After the 10 minutes, test if the marmalade is cooked by spooning a little of the marmalade onto a cold plate and placing it in the fridge.
If it sets into a jelly, it is cooked.
If not yet fully cooked, cook further for another 5-10 minutes and test the marmalade again.
Allow the marmalade to cool slightly and then pout into the sterilized jars.