Step 1

Hold each crab over a bowl as you prepare them to keep all the lovely juices. Use your fingers to find the triangular flap, lift and remove the whole top shell (keep the top shell of half the crabs to cook; this is purely for visual impact). Discard the feathery gills and place the crab on a board. Cut in half from top to bottom with a sharp heavy knife and lightly bash both large claws with the back of a cleaver to crack the shell. Repeat with remaining crabs, then refrigerate them, along with the reserved top shells. Refrigerate juice in bowl.

Step 2

Melt ghee in a large wide saucepan over medium heat, then add onion, garlic, ginger, chillies and curry leaves and fry, stirring occasionally, until onion is softened (5 minutes). Dry-roast curry powder in a frying pan until fragrant (1-2 minutes). Add to pan along with remaining spices and sea salt and stir regularly until you feel the spices starting to catch on the bottom of the pan (about 5 minutes). Mix in coconut milk and tamarind, add the reserved crab juice and bring to the boil, then remove from heat and cool to room temperature. Add crab pieces, mix well and refrigerate overnight.

Step 3

Bring crab mixture to room temperature. Place a very large (see note) saucepan on high heat and leave it until it becomes very hot so it retains heat when crab mixture is added, then add crab mixture and chopped coriander roots and stalks, let mixture start to sizzle, gently stir for a moment (this can be with such a full saucepan), then cover with a lid. Continue cooking covered, lifting lid to move the crabs about every few minutes, until crabs turn orange and are cooked through (about 20 minutes). Check seasoning, squeeze in some lime juice and serve hot garnished with coriander leaves.