Preheat the oven to 325°. Rinse the pork, scraping off most of the spices, and pat dry. Heat a large, deep ovenproof skillet until hot. Add the pork, fatty side down, and cook over moderately high heat, turning once, until browned on both sides, 8 minutes. Scatter the garlic, onion, celery and carrots on either side of the pork belly and cook until softened slightly, 5 minutes. Add the wine and boil until reduced to 1/4 cup, 5 minutes. Add the broth and bring to a boil. Cover and braise in the oven for 2 hours, until the meat is very tender but not falling apart. Transfer the pork to a platter and refrigerate for 30 minutes. Cut the meat into 1/2-inch-thick slices, then cut each slice in half so it will fit on the ciabatta.