Season beef chuck roast generously with salt & pepper. Set aside. In a large pot over medium heat, cook bacon for 3 to 4 min., or until golden brown and crispy. Transfer to a medium bowl. In batches, add beef to pot in an even layer and sear on all sides, about 5 min. per batch. Transfer beef to bowl with bacon. Add onion to the pot and cook until golden brown, about 6 min. Stir in garlic and cook for 30 seconds or until fragrant. Add beef stock, kidney beans, tomatoes, Mexican Mole, Mild Chili Powder, apple cider vinegar, and reserved beef and bacon. Bring mixture to a boil. Reduce heat and simmer gently, uncovered, for 2 to 3 hours, or until beef is fork-tender. Add dark chocolate and stir until melted. Season with salt & pepper to taste and serve.