The night before, soak the beans in cold water to rehydrate them.
Cook the beans in water with bay leaf and one pinch of salt for about 1 hour or until soft. If necessary, add more water while cooking.
Drain the beans, but keep the cooking water aside.
Finely chop the onion or shallot, and cook gently in a small pan on low heat with olive oilf or 3 minutes. Then add the beans and a pinch of salt, stir, and cook over medium heat for 3 minutes.
Put the veggies in the blender, add the saba (or balsamic vinegar), a tablespoon of olive oil, and two tablespoons of the beans' cooking water. Blend and reduce to a cream.
Then taste the cream, adjust the salt, and add more cooking liquid until the cream is soft as you want it.
Place the paté in a bowl, cover, and place in the refrigerator for 3 hours. Remove from refrigerator 1 hour before serving.
Reheat the terrine for three minutes, covered with aluminum foil, in a preheated oven(190C degrees or 374F). But you can eat it at room temperature.
Store in the refrigerator for several days.