Soak the borlotti beans in cold water overnight. Drain them and simmer in plenty of lightly salted water until tender but firm (al dente). Reserve the bean cooking liquid.
Peel and finely chop the onion. Sauté it in a large pot or Dutch oven with a drizzle of olive oil until soft and translucent, then transfer the onion to a plate and set aside.
In the same pot, brown the ribs over medium heat, turning them occasionally to ensure they are evenly browned on all sides. Return the sautéed onion to the pot and stir to combine.
Add the tomato passata, season with salt, and cook over low heat for 40 to 45 minutes, basting with a ladle of the bean cooking broth if the sauce reduces too much.
Add the cooked beans and sage leaves to the pot, then continue simmering for an additional 30 minutes until the meat is tender and the flavors have melded.
Garnish with a sprinkle of finely chopped rosemary, season with freshly cracked black pepper, and serve hot.