1. Soak etrog for one week, changing water daily.
2. Slice etrog and remove seeds. Place etrog slices in pan with water to cover. Bring to a boil. Drain. Repeat three to four times.
3. In small saucepan, bring sugar and water to a boil. Cook until sugar is dissolved. Pour over etrog, cover pot, and let stand at room temperature overnight.
4. Add quince to etrog. Cook for two to three hours or until liquid is absorbed.
5. Add lemon juice 10-15 minutes before done.