Soak the rice for 20 minutes in a small bowl of water. Strain the rice, then tip into a large mortar. Pound with a pestle until it becomes a sticky paste. Add the lemongrass, chilli and shallot and pound again. Add the dill, basil and spring onion and pound again. Add a pinch of sea salt, 1 tablespoon water, the padek orlmam nem and the lime leaves. Cut the fish into 2.5 cm (1 inch) pieces and add them to the mortar. Mix together with a large spoon. Soften the banana leaves, either over a gas fire, in a hot frying pan, or by steaming or microwaving them for a few minutes.Lay two banana leaves on the bench, at diagonals to one another. Place half the fish mixture in the centre, bring the corners together and enclose the corners to form a pyramid. Pin the edges together with toothpicks to secure the filling. Repeat with the remaining ingredients to make a second parcel.
Half fill a steamer, wok or large saucepan with water and bring to a rapid boil over high heat. Place the parcels in the steamer, fat side down, and steam for 20 minutes. Serve hot, with sticky rice.