1. Preheat oven to 350°. Remove and discard root ends and dark green tops of leeks. Thinly slice leeks; rinse well, and drain.
2. Tie pork roast with kitchen string, securing at 2-inch intervals. Season with salt and pepper.
3. Cook bacon in hot oil in an ovenproof Dutch oven or large, deep cast-iron skillet over medium-high heat 3 minutes. Add leeks, garlic, and onion, and cook, stirring frequently, 15 to 17 minutes or until mixture is golden brown; transfer to a bowl.
4. Add pork roast, fat side down, to Dutch oven, and cook 2 minutes on all sides or until browned. Remove pork.
5. Return leek mixture to Dutch oven; top with pork. Add broth and next 3 ingredients. Reduce heat to medium, and bring to a light boil. Remove from heat, and cover with heavy-duty aluminum foil.
6. Bake at 350° for 4 to 5 hours or until a meat thermometer inserted into thickest portion registers 195°. Remove pork from Dutch oven, cover with foil, and let stand 20 minutes. Shred pork with two forks.
7. Meanwhile, pour pan juices through a wire mesh strainer into a saucepan to equal 4 cups, discarding solids (add equal parts broth and white wine to pan juices to equal 4 cups, if necessary). Let stand 5 minutes; skim fat from surface of pan juices.
8. Bring to a boil over medium-high heat, and cook 20 to 25 minutes or until liquid is reduced to 1 cup and slightly thickened. Remove from heat, and stir in butter until melted. Serve with pork.