Season the beef cubes generously with salt and black pepper.

Heat the oil in a large heavy-bottomed pot or Dutch oven over medium-high heat. Sear the beef in batches until browned on all sides, then remove and set aside.

In the same pot, reduce heat to medium and add the diced onion. Sauté for 5 minutes until softened.

Stir in the minced garlic, chili powder, and cumin, cooking for another minute until fragrant.

Add the minced chipotle peppers, crushed tomatoes, and beef broth, scraping up any browned bits from the bottom of the pot with a wooden spoon.

Return the browned beef and any accumulated juices to the pot and bring the mixture to a simmer.

Cover tightly, reduce heat to low, and simmer gently for 2 hours, or until the beef is very tender.

Stir in the kidney beans and the piece of dark chocolate, simmering uncovered for an additional 15-20 minutes to thicken the sauce.

Taste and adjust seasoning with additional salt if needed before serving hot.