Soak the beans in cold water overnight or a minimum of 8 hours.
Drain and rinse the beans.
Put the beans in a heavy bottomed pan, cover with water, which should come about 3-4 cm above the beans, add some salt and cook gently for about 20 minutes. Drain.
In a separate pan heat the olive oil on a medium heat, add the garlic cloves along with the sage leaves.
Once the garlic starts to turn golden in colour add the drained beans to the pan, and after a few minutes the tomatoes. Season with some salt, pepper and add the sugar if needed.
Cook everything slowly until the beans turn soft.
Taste and season again before serving.