Preheat the oven to 275°F.
Add the pancetta to a large stockpot or Dutch oven and put it on the stove over low heat. Render the pancetta for about 10 minutes. (Rendering the pancetta slowly melts it, releasing all the fat and making the meat crisp.)
Turn the heat up to medium-low and add the sausage to the pot. Cook until it begins to brown, about 10 minutes. Then, moving the pancetta and bacon around the pot to make a bit of space, add the chicken legs and sear them in the pancetta and sausage fat and juices. Once they are becoming brown on all sides, reduce the heat to low, cover the pot and cook until the meat is cooked through, about 15 minutes.
Use a slotted spoon to remove all of the meat from the pot and add it to a large plate, leaving behind the fat.
Over medium-high heat, add the onions. Stirring every few minutes or so, cook the onions until they are very tender and are beginning to become brown, about 15 minutes. Add the roasted garlic and stir to blend.
While the onions are cooking, remove the chicken meat from the bones and break it into bite-sized pieces.
Add the thyme and paprika to the pot and cook for a couple minutes, until it’s very aromatic.
Add the olives, return all of the meat to the pot, and stir to combine. Then deglaze the pot with the tomatoes, wine and stock. Use a flat-bottomed wooden spatula to scrape any stuck bits of food from the bottom of the pot, back into the mixture.
Bring to a boil, then reduce the heat to medium-low and simmer to reduce the liquid by one third. This should take about 30 minutes.
Fold in the cooked cannellini beans and season generously with salt and pepper.
Pour the mixture into a baking dish that's approximately 9 X 13 X 2-1/2-inch.
Add the rosemary to the breadcrumbs and sprinkle the mixture evenly on top of the cassoulet. Drizzle the entire thing with olive oil and then bake, covered, in the preheated oven, covered with foil for 2 hours. Then uncover and place under the broiler to brown the top, about 1 minute.
Let it rest for at least 20 minutes before serving.