NOTE: + 12 hours soaking
Soak the beans in cold water for 12 hours. Remove the beans that float to the surface and drain and rinse the rest.
Put the beans in two litres of cold, unsalted water with the sprig of sage. Simmer over a low heat for about one hour, until sufficiently tender. Add salt when almost cooked.
Heat the oil in a wide, low pan with a couple of sage leaves and the freshly peeled and crushed garlic.
When the sage starts to wilt and the garlic to brown, add the tomato puree, cover and cook for 10 minutes.
Drain the beans, add them to the pan while still hot and stir gently. Adjust for salt and add plenty of black pepper. Cook for about 15 minutes and serve immediately after adding a drizzle of oil.