6 tablespoons (3/4 stick) butter
8 ounces pancetta, cut into 1/4-inch dice
2 large onions, finely chopped
2 carrots, peeled and finely chopped
3 celery stalks, finely chopped
2 tablespoons chopped fresh rosemary leaves
3 garlic cloves, chopped
2 (7.4-ounce) jars roasted peeled whole chestnuts, coarsely broken
1/4 cup chopped fresh Italian parsley leaves
1 pound day-old ciabatta bread, cut into 3/4-inch cubes
2/3 cup freshly grated Parmesan
1 cup (or more) canned low-salt chicken broth
Salt and freshly ground black pepper
2 large eggs, beaten to blend