Soak chopped dates in 2 and half cups of warm water for 45 minutes.
Dry roast cumin seeds and fennel seeds together. Grind it to a coarse powder and keep it aside
In a heavy bottom pan, add soaked dates along with water in which dates were soaked and jaggery.
Bring it to boil, add tamarind pulp, roasted cumin-fennel powder, black salt and sonth.
Simmer on low heat for 20-25 minutes. Dates should get soft after 25 minutes. Take it off the heat and cool.
Put the prepared chutney in blender and blend it to a pulse 2-3 times. Pour back into the pan and cook for another 6-8 minutes, consistency should be thick creamy but pourable. Add vinegar and mix well.Take it off the heat and cool completely.
Pour it in a clean air tight container and store it in a refrigerator for 3 months. Use it as and when required