Method:

1. Submerge the tamarind in half a cup of hot water. Set it aside to soak.

2. Heat a griddle or flat pan over a medium heat and gently roast (stirring often) the cumin seeds, peppercorns, and dry red chilies until they begin to darken and release a faint aroma. Set them aside to cool.

3. Heat the oil in a pan over medium heat and add the onions. Fry them until they soften and turn slightly golden.

4. In the bowl of a food processor, combine the onions with the turmeric, garlic, and ginger and grind them to a smooth paste.

5. Squeeze the soaking tamarind in the water with your hand to release the softened pulp. Do this until you release all of the pulp. Strain it and set the juice aside, discarding the solids.

6. Put the onion-spice paste back into the pan. Cook on medium for 1 minute, then add 1 1/2 cups warm water and the tamarind juice. Bring it to a boil, then reduce the heat to a simmer.

7. Add the prawns and cook just until they turn pink. Take care not to overcook them or they will become rubbery. Season the dish to taste with salt.