Crab in Pepita Sauce

To prepare crabs, break off tail flaps on the underside and discard. Cut each crab in half lengthwise, then carefully pull off back shells and reserve. Discard the 'dead man’s fingers' (soft gills), then rinse and discard stomach sac.
Melt butter in a large saucepan over medium–high heat. Add crabs and reserved shells, and cook, turning occasionally, for 6 minutes or until shells start to turn orange.
Meanwhile, blend tomatoes, capsicum, chillies, pepitas, garlic and coriander roots in a blender, then add 250 ml (1 cup) water and blend to a purée.
Add pepita mixture to crabs, bring to the boil, then reduce heat to medium and simmer for 12 minutes or until the crabs are cooked. Transfer crabs to a bowl and cover to keep warm. Increase heat to medium–high and cook pepita sauce for 4 minutes or until reduced by half. Discard shells and season sauce with salt and pepper.
Place crabs on a plate, spoon over pepita sauce, scatter with coriander and extra chillies, and serve with bread.