Heat the water in a kettle and pour it into a large pot. Alternatively, you can heat the water directly in the pot.

Peel and core the quinces, keeping the seeds aside. Cut the fruit into small cubes and add them straight to the hot water as you go to prevent browning.

Put the pot on the heat and bring the water to a boil. Simmer for 5–7 minutes, or until the quinces soften.

Once they soften, add the sugar and the reserved quince seeds. You can tie the seeds in a small piece of muslin to make them easier to remove later. Stir gently to help the sugar dissolve.

Reduce the heat to medium-low and let the jam simmer gently, uncovered, for about 1 hour and 10 minutes. Stir occasionally and skim off any foam that forms on the surface.

As the jam cooks, it will gradually thicken and change from pale yellow to a pinkish-red color.

Add the lemon juice and simmer for another 10 minutes. Remove the pot from the heat. Don't worry if the jam still looks a little runny. It will thicken further as it cools.

Remove the quince seeds. Transfer the jam to sterilised jars while it's still hot, or let it cool completely and then spoon it into sterilised jars. See the notes below for both methods and storage instructions.