Wash and wipe dry lemons thoroughly. Make deep slits crosswise without cutting the lemons. Place the lemons in a bowl, add salt and black salt (both in equal quantity), red chilli powder, garam masala powder (it should not contain coriander seeds), ajwain and mix well so that all the lemons are evenly coated with the masala.
Add sugar (half the weight of lemons) and mix well. Transfer the pickles into a porcelain container, cover it with a muslin cloth, secure with a string and keep it in sunlight for twenty five to thirty days to allow it to mature before using.