Prepare the prawns. Clean and devein the prawns. If making stock, keep the thoroughly cleaned heads and shells aside. Mom likes a mixture of tiny shrimp and medium prawns for both flavour and bite.
Make the green paste. Grind the coriander leaves, green chillies, ginger and garlic into a paste, adding only a little water if the mixer needs help.
Cook the masala patiently. Heat the oil in a pan and add the chopped tomatoes. Add the green paste and a little salt. Fry over medium-low heat for around 15 to 20 minutes, stirring regularly. There may be some splattering at first. Give it time to cook down.
Make the stock, if using. In another pan, sauté the cleaned heads and shells in a little oil. Add salt and 1 cup water. Boil for about 10 minutes, then let it cool enough to handle and strain thoroughly, discarding the heads and shells. Reserve a little stock for the prawn masala and use the rest as part of the rice cooking liquid.
Cook the prawns separately. Add the prawns to the cooked green masala, with a little stock or water if needed. Cook for around 5 minutes, or just until the prawns are opaque and cooked through. Adjust the salt and take the pan off the heat. Do not keep cooking them while the rice cooks.
Wash and soak the rice. Wash the basmati 3 to 4 times and soak for about 15 minutes. Drain well.
Prepare the rice liquid. Bring 3 cups of liquid to a boil and season with salt and the sugar. If using prawn stock, include it within those 3 cups, topping up with plain water. It is part of the measured liquid, not an extra addition.
Build the rice base. Heat the ghee in a heavy-bottomed pan. Add the cloves, cinnamon, bay leaves and optional peppercorns. After a minute or two, add the sliced onions. Cook until golden-brown or beginning to brown.
Cook the rice. Add the drained rice and gently sauté with the onions for a couple of minutes. Carefully pour in the boiling liquid and check the seasoning. Cover and simmer on low heat for around 10 to 15 minutes, until the rice is cooked and the liquid absorbed. Allow a little longer if the rice needs it.
Bring the two together. Gently fold the prawn masala into the cooked rice. Keep a light hand so the grains stay intact. The prawns have already cooked, so this is the final mixing step rather than another long simmer.