Wash the lemons and, working on a large dish to catch the juices, cut the fruit into slices, remove the pips and tie them in a muslin bag.
Put the fruit, juices, bag and water into a preserving pan, cover and bring carefully to the boil, simmer until the rind is soft
. Remove from the heat and add the warmed sugar, stirring well until it has dissolved.
Bring to the boil and reduce the heat to keep it just boiling. In about 10 minutes the jam will be cooked and thick.
Remove the bag, squeezing well and put the pulp through a liquidiser or mincer. Return to the pan.
Heat gently beating well with a wooden spoon to ensure that you have a soft smooth jam. Bring to the boil stirring continuously and taking great care not to burn it. Remove from the heat almost immediately.
Pot and seal.