Put the cut lime into a bowl and add the salt, mix it well, keep it for a day. Next day add mustard seeds, fenugreek, star anise seeds and chillies into a sauce pan, cover it and heat it well until the spices get roasted and mustard seeds start to pop. Remove the pan from heat. Drain the liquid from the lime into a small pan. Add sugar, ginger and water, boil it for 2 minutes until the sugar gets dissolved.
Mix the lime and spices and put into a clean dry preserving jar. Cover the lime with sugar solution. Let it cool, when it is cooled place the lid tightly. Keep it in a cool place for about 4 weeks. Mix it well before using.