Preheat the oven to 200°C.
Heat half the crab shell, chicken stock, lemongrass, and one lime leaf in a saucepan.
Roast remaining shell, red chilli, chopped shallot, tomato purée, and vegetable oil for 30 minutes.
Strain the roasted crab oil into a sterilized jar and set aside.
Sauté the finely chopped shallot and remaining lime leaf in butter until medium-hot.
Stir in rice, curry paste, and wine, cooking until the liquid is absorbed.
Gradually add strained crab stock to the rice over 15-20 minutes until tender.
Stir in coriander, green chilli, cream, and both types of crab meat.
Mix in parmesan, mascarpone, lime juice, and seasoning.
Plate the risotto, garnish with coriander cress, and drizzle with crab oil.