Quarter your quinces, removing any wormy looking bits. You can leave the peel and core in tact.

Place them in a large pot and add water just to cover.

Bring to a simmer and cook until soft, about 1 hour. Be sure not to cook more than 1 1/2 hours, or you will destroy the pectin and it won't gel.

Pour the fruit and juice through a fine mesh strainer into a bowl.

Set the fruit pulp aside.You can run it through a food mill if you'd like and make quince paste, quince butter, or serve it on toast.

Pass the liquid through the fine mesh strainer again, lined with cheesecloth, into a bowl.

Measure the liquid into a sauce pot. For each 1 liter (1 quart) of juice, add the juice of 1 lemon and 950 grams (4 3/4 cups) sugar. (You should get 1 liter of juice from about 1.8 kilos or 4 pounds quinces.)

If you prefer to use less sugar, then you will need to use pectin according to package instructions.

Cook the liquid rapidly at high heat skimming off scum until it reaches 220 degrees F at sea level. Don't go over 220 or it gets clumpy. Also be sure not leave it unattended because it will rapidly boil over.

Transfer it to sterilized jars and in a hot water bath for 10 minutes.