Place crabs in freezer for 1 hour to immobilise them, then kill each crab humanely by inserting a knife into the centre of the head and splitting through the middle. Pull off top shells, pull out the spongy grey gills and remove guts. Chop each crab into 6 pieces, then crack the large claws but leave attached.
Combine crab in a bowl with coconut milk, goroka, cinnamon, chilli powder, cumin, fenugreek and turmeric, stand for 20 minutes.
Heat ghee in a wide saucepan over high heat, add onion, ginger, curry leaves, lemongrass, chillies and pandanus, cook until onion is golden (5 minutes). Add dill seeds, cook another 2 minutes, add crab mixture. Cover and simmer until crab is just cooked through and sauce has thickened (12 minutes). Pick out crab meat (or use whole crab pieces) then return picked meat to sauce. Add coriander, murunga and lime juice, season to taste with salt.
Note Pandanus, murunga and goroka are available from Asian grocers. Murunga leaves are commonly known as drumstick leaves in Australia. If unavailable, substitute 2 tbsp chopped parsley and an extra squeeze of lime. Ghee is available from select supermarkets. This recipe is from Serendip: My Sri Lankan Kitchen by Peter Kuruvita (Murdoch Books, $59.95, hbk). In editing these recipes for publication, we have made minor changes to bring them into Gourmet Traveller style.