Make the pickling liquor. Put all the ingredients in a heavy-based saucepan over a low heat and stir occasionally until all the sugar dissolves. Remove from the heat and set aside to cool before decanting into a sterilised jar. Store in the fridge until required.
Make the pickle. Peel the turmeric root into thin ribbons, and place into a bowl. Steep in the pickling liquor for one to two hours at room temperature, then keep in the refrigerator until needed.
Prepare the langoustines by cutting lengthways down the centre of each, keeping the head intact, and removing the intestinal thread. Marinate in the oil, turmeric and salt, then cover and set aside in the refrigerator.
Make the lasooni butter by blitzing the butter in a food processor with the coriander, garlic, green chillies, a squeeze of lime juice and salt.
Grill the langoustines under a high heat for two to three minutes on each side until just cooked. Alternatively, you can also cook the langoustines in a heavy-based frying pan over a medium to high heat. Ensure you do not overcook them.
Melt the lasooni butter gently in a small frying pan to retain its vibrant colour. Squeeze in little more lime juice, then spoon it over the cooked langoustines. Garnish with pickled turmeric and serve.