Dry roast the red chillies and set aside.
In the same pan,dry roast coriander seeds, cumin seeds, ½ tsp mustard seeds, carom seeds, methi seeds, and peppercorns until aromatic. Remove and let cool.
Once cooled, grind the roasted spices along with one chopped onion, garlic, tamarind, grated coconut, and a few curry leaves to a fine, smooth paste. Add a little water if needed.
Heat oil in a pan (a clay pot enhances the flavour beautifully).
Add 1 tsp mustard seeds, the remaining chopped onion, and curry leaves. Sauté for a few seconds.
Add the prepared masala paste and mix well.
Add salt and water as required, keeping the curry slightly thick. Bring to a boil.
Once the curry starts boiling, add the prawns,mix gently, cover, and cook for 5–6 minutes.
Do not overcook the prawns Serve hot with Kappa Rotti, Neer Dosa, or steamed rice.