2tablespoonstamarind pastemore or less depending on the sourness you like
salt to taste
Heat the oil in a heavy bottom saucepan on medium heat. Add mustard seeds and allow them to splutter. Add fenugreek seeds and onions. Saute for a minute and add green chili along with half the curry leaves. Continue to cook for 5 minutes over medium heat until the onions begin to change color to a light brown.
Make a fine paste of ginger, garlic, and dry red chili in a blender and add it to the pan. Add turmeric powder and mix well.
Add tomatoes and continue to cook until they soften for 5 minutes. Add water along with tamarind paste and mix well. Lower the heat and bring to simmer for 2 minutes.
Add shrimp and cook covered over low heat for 5 minutes stirring halfway through. Turn the heat off and add the remaining curry leaves and cilantro. Serve with steamed Basmati rice.