1. Place the tamarind along with the water in a microwave safe bowl and heat on high for about 10 to 15 seconds until the water is warm.
2. Extract tamarind juice by pressing the tamarind and pour into another container or bowl and keep aside, discard the pulp and seeds of the tamarind.
3. Heat oil in a heavy bottomed pan and when hot lower heat to medium and add black gram lentil to it.
4. When the black gram lentil turns reddish add the dry red chillies and asafoetida and saute once.
5. Immediately add the onions and saute until onions are almost transparent.
6. Add the tamarind juice to this and let it boil until the juice is almost boiled down to a thick consistency.
7. Cool this mixture and grind in food processor or blender until it is a smooth puree.
8. Add salt to this and mix well. Serve as required
9. This thogayal can be refrigerated and used within 3-4 days.

Courtesy: http://veginspirations.blogspot.com/