Skin, de seed and chop up the marrow into little cubes.
Weigh out 5 1/2 lb.
Sprinkle with the salt and forget it for 12 hours.
Now strain well.
Sprinkle on all the sugar and put aside for a further 12 hours.
Finely peel the lemons and put the rind and juice into a large saucepan with the marrow, sugar and chopped ginger.
Boil altogether until the marrow is golden and translucent and the jam sets on a cold plate.