Preheat oven to 350 degrees F.
Butter a 15 by 10 by 2-inch glass baking dish. Melt 2 tablespoons of butter in a heavy large skillet over medium heat. Add the pancetta and saute until crisp and golden, about 10 minutes. Using a slotted spoon, transfer the pancetta to a large bowl. Melt the remaining butter in the same skillet over medium-high heat. Add the onions, carrots, celery, rosemary, and garlic. Saute until the onions are very tender, about 12 minutes. Gently stir in the chestnuts and parsley. Transfer the onion mixture to the large bowl with the pancetta. Add the bread and Parmesan and toss to coat. Add enough broth to the stuffing mixture to moisten. Season the stuffing, to taste, with salt and pepper. Mix in the eggs.
Transfer the stuffing to the prepared dish. Cover with buttered foil, buttered side down, and bake until the stuffing is heated through, about 30 minutes. Uncover and continue baking until the top is crisp and golden, about 15 minutes longer.
Whisk the first 7 ingredients in a large bowl to blend. Stir in the Parmesan and bread crumbs. Mix in the beef, pork, and veal. Pack half of the meat mixture into a 9 by 5 by 3-inch loaf pan. Spoon the stuffing over the meat in the pan, leaving a 1-inch border around the edges. Top with the remaining meat mixture, enclosing the stuffing completely and pressing firmly. Spoon the marinara sauce over the meatloaf, then sprinkle with the provolone cheese.
Bake, uncovered, until the meat loaf is firm to the touch in the center and has pulled away from the sides of the pan, about 45 minutes. Cut crosswise into slices and serve.