First, wash the sweet potatoes well.
Place the potaotes in a pressure cooker. Add water just about covering the potatoes. Pressure cook for 2 to 3 whistles or till the potatoes have cooked completely.
While the potatoes are cooking, in a separate pan, dry roast 4 tablespoons of urad dal, 4 to 6 kashmiri dry red chilies, 2 peppercorns at medium heat, until the urad dal turns golden brown. Turn off the heat, add the asafoetida and mix. Then transfer these ingredients on to a plate and allow them to cool.
Once the cooker with the sweet potatoes has cooled down, open the lid, check using a fork to make sure the potatoes are cooked through. If well cooked, transfer to a plate and peel once cool enough to handle.
Mash them well. Allow to cool.
Once the spices also have cooled, add them to a mixer grinder, add 4 tablespoons of grated fresh coconut, 1 teaspoon of tamarind concentrate, pulse a couple of times without adding water to break down the spices.
Once they break down to a rough mixture, add the cooked mashed sweet potato, salt to taste.
Grind for a very short while so that everything gets mixed.
Then add ¼ to ½ cup of water and grind again until it forms a smooth paste.
Make sure to add small amounts of water to bring it to the right consistency (thick dropping consistency)
Transfer to a bowl.
Prepare tempering by heating 2 teaspoons of oil in a small pan.
Add mustard seeds and allow them to splutter. Add asafoetida (hing).
Turn off the heat. Transfer the tempering to the chutney.
Serve sweet potato chutney with roti/chapati/rice or as an accompaniment.