Peel the skin off the eggplants. If bitter, soak in water overnight.
Place eggplants in a large saucepan and cover with water, bring to boil then change the water to remove bitterness.
Again cover with fresh water, bring to boil then lower the heat to a simmer, add sugar, cinnamon sticks, cloves, and optional cardamom. Simmer for 20 minutes.
Remove from heat, cover with a lid, and let the mixture sit at room temperature until the next day.
On the next day, place the saucepan or pot with the jam on medium heat for about 20 minutes and allow to simmer. Remove from heat.
On the third day, repeat the same steps as the second day, adding the juice of one lemon and walnuts before removing from heat. Let the jam sit for about 20 minutes.
Pour into sterilized jars and seal.