Set a shelf in the lower third of the oven and preheat the oven to 300 degrees . If the pork shoulder came wrapped in elastic netting, remove it.
In a large Dutch oven (5- to 6-quart) or other heavy pot over medium heat, cook the bacon in the olive oil until crisp, about 7 minutes. Use a slotted spoon to remove the bacon and set aside. Pat the surface of the pork dry with paper towels. Season the pork all over with salt and pepper. Carefully place the pork in the Dutch oven and sear on all sides until browned but not burnt, about 20 minutes. Transfer to a large plate.
Pour off and discard all but 1 tablespoon of the fat and return the Dutch oven to medium heat. Add the leek, season with salt and cook, stirring once or twice, until softened but not browned, about 3 minutes. Add the garlic, coriander, paprika, oregano and red pepper flakes and cook 2 minutes. Stir in the tomato paste and cook for 1 minute.
Return the pork and any juices to the pot. Scatter the reserved bacon over the pork. Bring the liquid to a simmer and spoon some of it over the pork. Crumple a large piece of parchment paper and place it over the meat, pressing down so that it almost touches the meat and the edges extend over the sides of the pot by about an inch. Set the lid in place and slide the pot into the oven. After 30 minutes, check that the liquid is simmering gently, and turn the roast. Continue braising until the pork is fork-tender, about 2 1/4 hours.
Pour the wine into the pot and bring to a boil, stirring and scraping the bottom of the pot with a wooden spoon to release any brown bits, until the liquid is almost evaporated, about 2 minutes. Add the broth and boil for 2 minutes, scraping the bottom of the pot with the wooden spoon. Trim the ends off the orange, then cut it in half. Place flesh side down and slice into 1/4-inch-thick half-moons. Add the slices to the broth and boil for another minute.
Remove the pork from the pot and set it on a carving board or platter to catch the juices. Cover the roast loosely with foil. Skim off as much fat as you can from the cooking liquid and taste the sauce. If it seems thin, simmer to reduce and to intensify the flavor. Season the sauce with salt and pepper.
Remove the strings from the pork and cut it into 1/2-inch-thick slices. Arrange the pork on a serving platter. Pour any juices into the sauce. Stir the parsley into the sauce and spoon it over the meat.