Clean prawns, wash them well and set aside.Take all roasting spices in a heavy bottom pan and toast them till golden. Cool them down and take them in a blender. Powder them and set aside.Now in the same pan, add oil and heat it up. Add in mustard seeds, asafoetida and curry leaves.
Add in shallots and saute till golden. Add in tomatoes and green chillies. Cook that down till it gets mushy.
Add in spice powders and the ground masala. Mix well. Add salt and tamarind pulp to taste.
Add enough water to make a gravy. Simmer this till oil separates
Now add in prawns and mix well. Simmer for 10 mins or so.