Soak the mahali roots in water for at least an hour.
While the roots are soaking, grind together the mustard seeds and red chillies along with the salt and turmeric powder. Transfer to a large and completely dry mixing bowl. Mix well.
Now scrub the mahali roots clean, and scrape off the outer peel. Slice them lengthwise to expose the tough inner “vein” and discard it. Chop the cleaned mahali into small bits.
Keep dropping the bits into the bowl with the mustard-chilli-turmeric-salt. Mix with a spoon to coat and prevent discoloration.
Now add the lime juice and mix well.
Transfer this into a sterilized (or cleaned in hot, soapy water and then dried completely in an oven) pickle jar. Close the lid and keep this in a warm spot on the kitchen counter for 3 days.
Open the jar daily and mix with a clean, dry spoon. Alternatively, just shake the jar vigorously every day.
After 3 days, you have 2 choices. You can add the fresh curd to the pickle and then refrigerate. The curd will sour slowly in the fridge and you can consume the pickle a little at a time.
If you are concerned about how much souring will happen after the curd addition (especially if you consume the pickle only occasionally, as we do), then your second option is not to add the curd but simply refrigerate the cured mahali pickle. When you are ready to consume it, take a small quantity of the pickle and add a few spoons of sour yogurt to it. Leave it for anywhere from a few hours to a day to cure further. Serve this with your meals and store it separately, mixing in more of the cured mahali root and curd as you use it and as needed.