Soak the tamarind in about 3 cups warm water for about half an hour. Using your fingers, rub the tamarind well in the water and then squeeze out as much pulp as possible. Throw away whatever residue is left of the tamarind and keep the tamarind pulp aside.
In a deep pan (or wok), heat the sesame seed oil. Add the mustard seeds. When they splutter, add the lentils and saute till they’re golden in colour. Turn down the heat to medium and add the asafetida powder and the curry leaves. Stir a couple of times and add the chopped ginger, green chillies and turmeric powder.
Saute for about 5 minutes till the ginger turns soft. Add the tamarind pulp, jaggery and salt and bring to a boil. Turn the heat a bit further, and simmer till the mixture thickens to the consistency of a chutney and you can see a bit of oil on the surface.
Take off the heat, cool and bottle. This recipe makes a small jar of chutney and will keep for over a month.