Soak the beans the night before. Change the water and boil with a sprig of sage and a couple of cloves of garlic for 1.5 hours (or pressure cook for 20 minutes), until tender.
Wash the carrots and celery, peel the carrot and dice everything.
Dice the onion.
Put the diced onion, carrots and celery into a large pot soften on a low flame for 5-10 minutes in a good swirl of olive oil.
Wash and slice the savoy cabbage, add to the pot and wilt.
Meanwhile, peel the potatoes and dice them.
Add the potatoes and the cavolo nero to the pot and cook for a couple of minutes, stirring well to avoid sticking. Slice the mushrooms and add.
Add the hot stock. Stir well.
Season with salt and pepper, bring to the boil and cook on a brisk flame for 20 minutes.
Lower the flame, add the beans, half whole and half pureed, and cook on a simmer for 30 minutes, You may need to add extra stock or hot water to keep the vegetables always covered. Add the pasta in the last 10 minutes of cooking time.