For the Sri Lankan curry powder, roast each ingredient except the curry leaves and chilli powder separately in a dry frying pan over a low heat until fairly brown but not burnt. Place all the roasted ingredients and the curry leaves and chilli powder in a spice grinder, grind to a fine powder. Store in an airtight container (you might prefer to grind just the 2 teaspoons needed for the recipe, as whole spices keep much better). For the curry, peel the shells off the prawns (if they are in their shells), leaving the heads attached. Run a small sharp knife down the back and remove the vein, then rinse. Mix the lemon juice, garlic, ginger, salt, black pepper, 2 teaspoons of Sri Lankan curry powder and red chilli powder together in a bowl. Rub the mix onto the prawns and refrigerate (don’t leave for longer than 1 hour or the prawns will ‘cook’). Heat the oil in a large frying pan and fry the curry leaves until fragrant and crisp. Remove from the pan and set aside on paper towels. In the same pan, sear the prawns for 4–5 seconds on each side, then remove from the pan and set aside. Add the onion to the pan and cook until soft, adding a touch more oil if needed. Add the cinnamon, cardamom and cloves. Cook for another minute or so, then add the tomato paste and stir for 1–2 minutes. Add the fish stock and bring back to the boil, then add the coconut cream and bring to the boil without covering. Finally, add the prawns back in and simmer for 1–2 minutes until cooked through. Taste and adjust seasoning with salt. Remove the cardamom pods, cinnamon stick and cloves. Top the prawns with fried curry leaves and serve with steamed rice.