If possible use "Bousserra" or "Doq" lemons. These lemons are big, golden yellow and rich in juice. But any lemon really would do.
Prepare preserved lemons in spring when the fruit is ripe and golden yellow. Wash the lemons in a bucket. Divide the fruit into 4 quarters, take care to leave the pieces joined at the stalk end. Salt the inside carefully and generousely, put together again and place in a preserving bottle or jar, which has never been used for fatty foods. Cover right up to the top with moderately warm water, put a perfectly clean stone on the fruit if you're using the jar and cover, or just close up the preserving bottle. Store in a dry place. One month later the lemons are ready for eating. These lemons are used for flavoring tajines. Just before using, throw the inside part away, wash and use only the zest cut in quarters. You will probably notice a white cream on the lemons but it is normal, wash it away for aestetics.