I seem to be unable to make the correct amount of marmalade each January, as either I have too much left when the Seville oranges come in again, or I run out, as I did last year and have this. As I am not very fond of three-fruit marmalade, finding it rather too sweet and lacking the "tang" or a proper Seville orange marmalade, I made lemon marmalade last year, and have done the same this year.
4 lemons and their weight in sugar, and the equivalent amount of water, or a little more (my lemons weighed 540 g so I used 600 mls of water and 600 g sugar).
Place whole lemons into a pressure cooker with the water and cook on HIGH pressure for 20 minutes, then allow to cool. Remove lemons from the water, then remove the insides, which you return to the water, and chop the peel as finely as possible. Boil up the water with the insides of the lemon in it for 5 minutes, then strain to remove the pips. Add the chopped peel and sugar, and heat gently until the sugar has dissolved. Then boil hard until setting-point is reached (about 5 minutes - lemons have a lot of pectin!).
Allow to cool for 10 minutes or so, then pot into heated jars, cover and seal. Keeps indefinitely, but you only need it to keep until you make proper marmalade again in January!