Wash and roughly chop the quinces
(no need to peel, decore or depip) and place in a heavy bottomed saucepan. Barely cover with water. Bring to the boil and simmer gently with a lid on until soft. If the quinces are very firm this could take several hours. Check it every now and then and add more water if necessary. Pour the cooked fruit through sterilised muslin into a large clean bucket or bowl, I hang my jelly bags up in the kitchen above a bowl, some people like to get all fancy with chairs or stalls, I’m limited by space.
Leave the jelly bag to drip overnight (or about 12 hours).
Measure the juice the next day, Pour the juice into a deep heavy bottomed saucepan and add 1lb/454g of white granulated sugar for each 1pt/570ml of juice. Add the lemon juice. Heat everything, gently stirring from time to time,boil for about 10 minutes before testing for a set. Test every 3 to 5 minutes until setting point is reached. When jelly has reached setting point pour into warm sterilised jars using a funnel and ladle. Cover immediately with plastic lined screw top lids or waxed disks and cellophane tops secured with a rubber band. If you don’t think that the jelly has set properly, you can reboil it the next day. The boiling reduces the water in the jelly. I have done this in the past. Ideally you should try for the right set the first time.
Label when cold and store in a cool, dark place. Away from damp. Eat with toast!!!