Rose and prawn coconut curry

Ingredients

• 750g large green king prawns, shelled and deveined with the tails remaining
• 1½ teaspoons turmeric
• Juice of one large lime
• ¼ teaspoon salt
• 6 tablespoons vegetable oil
• 1½ teaspoons cumin seeded
• 1½ teaspoons mustard seeds
• 8 curry leaves
• 2 to 3 shallots, peeled and thinly sliced
• 3 cloves garlic, finely chopped
• 25g piece fresh ginger, chopped or grated
• 1 long green chilli, finely chopped
• 300ml fish stock
• 1 x 400ml tin full-cream coconut milk
• 140g tomato purée
• 1½ to 2 teaspoons natural rosewater essence
• ¼ teaspoon cayenne pepper
• 3 tablespoons chopped coriander leaves plus extra to garnish
• Salt to taste