Heat a heavy large Dutch oven over medium heat.
Add diced pancetta and saute until crisp. Using a slotted spoon, transfer the pancetta to paper towels to drain.
Sprinkle the ribs with salt and pepper.
Working in batches, brown the ribs in drippings in pot over medium-high heat until brown on all sides, about 8 minutes per batch. Transfer the ribs to a plate.
Add the diced onions, shallots, carrots, celery, and garlic to the pot. Cover, reduce heat to medium, and cook until vegetables are soft, stirring occasionally, about 10 minutes.
Add the red wine. Boil uncovered to reduce until liquid is reduced by half, scraping up browned bits, about 5 minutes. Add the broth, diced tomatoes, parsley, thyme, bay leaf, and pancetta. Stir to combine.
Return the ribs to the pot, cover partially, and simmer for 1½ hours.
Uncover and simmer until rib meat is tender, stirring occasionally, about 1½ hours longer
Transfer the ribs to a plate; discard the bay leaf.
Spoon fat from the surface of the sauce. Boil the sauce until beginning to thicken, about 8 minutes. Reduce heat to medium.
Add chocolate, cocoa powder, and rosemary, stirring until chocolate melts.
Season to taste with salt and pepper. Return the ribs to the pot. Simmer to rewarm, about 5 minutes.