Drain the beans, cover with fresh water and bring to the boil. Turn down to a simmer and cook for 1½-2 hours until the beans are just tender.
Gently soften the onion and garlic in 2 tablespoons of the olive oil for 5 minutes. When soft, stir in the paprika, tomato purée, chopped tomatoes, 100ml/3½fl oz water, salt and pepper.
Bring to the boil then reduce to a simmer and cook for 30 minutes. Stir in the chard and take off the heat.
Preheat the oven to 160C/140C Fan/Gas 3.
When the beans are cooked, drain them and mix with the tomato and chard sauce, adding a further 2 tablespoons of olive oil and the chopped herbs.
Transfer the beans to a casserole pan, drizzle with the remaining olive oil and bake for 35–40 minutes until the beans are tender and the sauce thickened and bubbling. Serve hot, warm or at room temperature.