Toast dried chilies in a dry pan until fragrant. Remove from heat, soak in warm water for 10 minutes, then blend into a smooth paste.
Heat vegetable oil in a skillet over high heat. Sear the beef cubes until browned on all sides, then transfer to the slow cooker.
In the same skillet, sauté onions and garlic until soft. Stir in cumin, smoked paprika, oregano, and cayenne, cooking for another minute.
Add tomato paste, beef broth, crushed tomatoes, and chili paste to the slow cooker. Stir well to combine.
Cover and cook on low for 8 hours until beef is fall-apart tender.
Stir in dark chocolate, letting it melt into the chili for extra richness.
Serve hot with your choice of toppings.