Mix the kecap manis, black beans, sugar and 3 tablespoons water together in a bowl and set aside. Heat 75ml oil in a large wok.

Add pieces of crab and stir-fry for 3 minutes, until the crab is half cooked. Lift the pieces out into a bowl and pour away all but one and a half tablespoons of the oil.

Return the wok to a medium heat, add 4 of the sliced spring onions, the ginger, garlic and curry leaves and stir-fry gently for 1 minute, taking care not to let anything brown. Add the black pepper and, after a few seconds, the black bean mixture. Return the crab pieces to the wok, turn over once or twice to coat in the
mixture, then cover with a lid and leave to cook for 5 minutes if the crab is raw, 2–3 minutes if using cooked crab.

When the crab is cooked, uncover and add the butter and sliced red chilli to the wok. Turn over once more to coat the crab in the sauce, then spoon onto 1 large serving plate or 2 soup plates, scatter with the remaining spring onion and serve.