If using dried beans, put them in a big pot, pour in cold water to cover by at least 10cm, add the bicarb, garlic and herbs and bring to a boil.
Turn down to a simmer and cook until tender – anywhere from one to two hours, depending on how recently the beans were harvested. If using tinned, omit this stage.
Meanwhile, warm the oil in a deep, heavy pan on a medium-low heat, add the onion, carrots, celery, garlic and half the parsley, and season generously. Leave to sweat, stirring from time to time, for 15-20 minutes, until the vegetables are very soft.
Bring a deep pan of salted water to a boil and blanch the cabbage until tender, about five minutes. Turn off the heat, but leave the cabbage in the water.
Stir the tomatoes into the onion mix, breaking them up with the spoon as you do so, add four to five tablespoons of the cabbage cooking water and leave to cook for 10 minutes more.
Whizz half the beans with a stick blender, until smooth and creamy (loosen with a few tablespoons of the bean cooking water, or tap water), then reunite with the whole beans and stir the lot into the soup pot.
Add the cabbage and bread, add enough cabbage water just to cover the veg, and season generously. Bring to a boil, turn down to a simmer and leave to cook gently for 20-30 minutes.
Spoon the rich, thick soup into bowls, scatter over the remaining parsley and drizzle with lots of good extra-virgin olive oil.