Wash the quinces well and remove the fuzzy layer if necessary. Mine did not have a layer, so just wash them well. Quarter the quinces and remove the pits and seeds. Leave the skin on.
Grate the quince with a grater or use a food processor. The latter is preferable because the quince is hard and grating it by hand is a chore.
Once grated, place the quince in a large saucepan and add the lemon juice. Add a liter of water and bring to a boil.
Let it simmer for about 10 minutes. Then add the sugar and cardamom seeds and let them dissolve well. Let the quince simmer gently for about 50 minutes to an hour. The color will slowly turn pink.
Want to test the jam? Place a saucer in the freezer and let it get very cold. Put a teaspoon of your jam on the saucer and run your finger through it. If the line remains intact, your jam is ready.