Heat the olive oil in a large casserole or heavy-based pan. Add the sausages and lightly brown them all over. Transfer to a plate and set aside.
Meanwhile, thinly slice the onion and garlic. Chop the carrot, chilli and rosemary.
Add the onion, garlic, carrot, chilli and rosemary to the pan and gently sauté for about 5 minutes, until the vegetables begin to soften.
Add the tomato purée and stir for about 30 seconds. Pour in the passata and water, then crumble in the stock cube. Bring to the boil.
Halve the potatoes if they are small; cut larger ones into bite-sized pieces. Add them to the casserole and reduce the heat. Cover and simmer gently for about 15 minutes, or until the potatoes are almost tender.
Return the sausages to the pan and add the chopped Savoy cabbage or cavolo nero. Simmer for a further 8 minutes, or until the potatoes are completely tender and the sausages are cooked through. If using spinach, add it for the final 2–3 minutes instead.
Add a little more water if the sauce becomes too thick. Season with freshly ground black pepper to taste.
Scatter with the chopped fresh basil or parsley and serve hot with crusty bread and a green salad.