Put some tea saucers in the freezer so you can test if the jelly is set later on.

To sterilise the jars you can plunge them in a large pan of boiling water for 10 mins. Alternatively you can also wash them in warm soapy water, rinse them and put them on a baking tray in the oven heated up at 100°C/225°F/gas ¼ for 10 mins. Make sure everything is very clean. You do not want to do this too far in advance as the jars should be warm when the jelly is poured into them.

Wash and core the quinces. Put the cores and seeds in a square muslin. Tie the muslin together with string to make a small bag.

Dice the quinces and place in a large saucepan with muslin bag. Pour water so that to cover fruits.

Bring to boil and cook under medium heat for 45-55 mins until the fruits are soft.

Remove the pan from heat. Drain the fruits once the mixture has cooled down. Some recipes call to leave fruits to drain in a muslin overnight. I usually do not bother with that. Instead I place the cooked quinces in a colander over a large salad bowl and mash them to collect as much juice as possible. I also squeeze juices out of the muslin bag.

Keep the mashed quinces to make quince paste if desired (see link above).

Measure out how much juice you have. Place in a large saucepan with equal volume of jam sugar. Add 1 lemon juice. Bring to the boil, stirring to dissolve the sugar. Boil until set (around 30 mins).

To test if the jam has set, put a teaspoon of jelly on one of the cold saucer. Let it cool for a minute. The jelly is done when it wrinkles when pushed with your finger.

Pour jam in the sterilised jars. Cover with waxed paper and seal.

Store in a cool and dry place away from the light. Once open keep in the fridge.