Grind in vinegar
a few garlic leaves
1 inch piece ginger
50 gms cumin seeds
5 gms mustard seeds
5 gms red chillies, deseeded
1/2 tsp tumeric powder
salt to taste
1. Smear half the quantity of the ground vinegar masala over the prawns and keep aside for 2 hours.
2. Heat oil in a pan and fry onions till brown. Remove and keep aside.
3. Now fry the prawns in the same oil, adding the remaining vinegar masala to it. Cook on a low flame till half done.
4. Then add the tomatoes, fried onions and potatoes and cook on slow fire, adding water if necessary.
5. Serve hot, garnished with slit green chillies.