To peel the tomatoes, bring a large pan of water to the boil. Add the tomatoes and simmer for 1–2 minutes, to loosen the skins, then drain and run under cold water. Peel and discard the skin, then roughly chop the tomatoes and set aside.

Pour the oil into a large, deep frying pan over a low heat. Add the shallots and fry for 5 minutes until soft. Stir in the ginger and garlic and fry for 10 seconds. Add the curry paste and tomato purée, and stir in the chopped tomatoes, lime leaves and lemongrass. Cover with a lid and bring to the boil. Reduce the heat and simmer for about 10–12 minutes, until the tomatoes are soft and broken down.

Remove the lid and boil to reduce the sauce slightly so it thickens. Stir in the sugar, fish sauce, lime juice and prawns. Season well with salt and ground black pepper and cook for about 5 minutes, or until the prawns are cooked and pink. Add the spinach and stir for a minute until wilted.

Serve at once with boiled rice.

Mary’s Tips: The tomato base can be made up to 6 hours ahead. Reheat the sauce and add prawns and spinach to serve. Not suitable for freezing.