2 kg sugar
Chill a saucer in the freezer, ready for checking the setting point of your jam. Wash the lemons and remove the top ‘button’ which would have been attached to the stalk. Put the lemons in a large saucepan with 2.5 litres water. Bring to the boil, then cover the pan and simmer for 2½ hrs or until the lemon skins are lovely and tender, and can be pierced easily with a fork.
When the lemons are cool enough to handle, remove from the saucepan. Measure the cooking liquid – you’ll need 1.5 litres in total. If you don’t quite have this, make up the difference with water. If you have too much liquid, bring to the boil and reduce to the required amount.
Halve the lemons and remove the pips – reserving the pips and any lemon juice that oozes out during the process. Cut the lemon peel and flesh into strips, as thick or thin as you like. Put all of this, including any juices, back into the pan. Put the pips in a small piece of muslin and tie up with string. Add this to the pan, as the pips will aid the setting process of the jam.
Add the sugar and bring to the boil, stirring until it has completely dissolved. Boil rapidly for about 20 mins until setting point is reached. Test the setting point by dropping a little marmalade onto the chilled saucer, allowing it to cool for 1 min, then pushing gently with your finger. If the marmalade crinkles, the setting point is reached; if not, continue to boil and check again in a few mins.
Leave to cool for 10-15 mins (this will prevent the lemon shreds sinking to the bottoms of the jars), remove the muslin bag, then gently stir in one direction to disperse any scum (small air bubbles on the surface). Pour jam into warm sterilised jars and seal straight away.