Peel the taro stolons the previous day. The brown covering has to come out totally. Chop the stolons into index-finger sized pieces. Wash properly and marinate with 2 tsp salt and lemon juice, for about 20 min. Blanch these in salted boiling water (with a little turmeric powder) for 10 min, or until the Loti are partially softened, but hold their shape firmly. Drain the liquid completely and reserve the Loti. Store in the refrigerator.
The next day, take out the Loti and let it come to room temperature.
Wash thoroughly and wipe the banana leaves (now a total of 10 leaves). From the middle, slit away the thick portion, so that each leaf is straight. Keep aside.
Marinate the prawns for around 20 min with 1 tsp salt and ½ tsp turmeric powder.
In a deep bowl, add the marinated prawns (minus the marinade), the onion, garlic and the coconut pastes, mustard oil, green chillies, nigella seeds, mustard seed paste and salt (according to taste). While adding salt, please note that the mustard paste, Loti and the marinated prawns already have salt in them. Add the salt accordingly.
With the help of a kitchen spoon, mix the above Paturi mixture very well. Now add the partially cooked Loti. Mix very carefully, so that the Loti pieces don’t lose their shape.
Take a non-stick pan (Pan No. 1). Brush oil over it. Put five banana leaves over it, one over the other. Make sure that the glossy sides of the banana leaves are facing up. Now spread the whole Paturi mixture over the topmost banana leaf.
Now cover this mixture from the top with an inverted banana leaf (glossy side down). Place the rest of the four banana leaves one over the other over this inverted banana leaf. All these leaves on the top must face down.
Cover the Paturi setup with a heavy pan (Pan No. 2) inverted over the topmost banana leaf.
Heat the Pan No. 1 on a medium flame. After 20 min, very carefully, invert the whole setup, so that Pan No. 2 is down and Pan No. 1 is on the top.
Heat Pan No. 2 for 20 min on a medium flame.
After 20 min, invert the setup again so that Pan No. 1 is down again. Slow-cook/simmer for about 10 more minutes. Open a corner of the wrap and taste one piece of cooked Loti. It should have softened completely by now (but should retain the shape).
Switch off the gas give the Paturi a standing time for 10 more minutes. Remove the pan on the top. Remove the top five banana leaves. Serve the Paturi with steamed rice. (I love to add around 2 tsp of raw mustard oil over the Paturi just before I serve this with rice.)