In a large braiser or cast iron Dutch oven, sauté the onion, carrot and celery in olive oil until soft and translucent. Add a good dollop of tomato concentrate, mix it with the aromatic vegetables and let it cook for another minute or two.
Now add the ribs, sausages and, if using, other pork parts to the pot and turn them in the aromatic vegetables. Gently simmer everything together for a few minutes, seasoning with salt and pepper. Pour over a drizzle of red wine and let it evaporate.
Now add the Savoy cabbage leaves and give it a turn. Moisten with perhaps 500ml (2 cups) water (or broth). Simmer, stirring from time to time, for an hour and a half, or until everything is perfectly tender and the liquid is well reduced. The cassouela should have the consistency of a thick stew, not a soup.
If needed add more liquid to the pot to keep things moist. If on the other hand, the stew is still brothy when the meat is tender, turn up the heat and cook off the excess liquid.
Serve hot. It's even better reheated after an overnight rest.