Step 1: In a large skillet or Dutch oven, heat the olive oil over medium-high heat. Add the ground beef and cook, breaking it apart with a spoon, until browned. Drain any excess fat.
Step 2: Add the chopped onion to the skillet with the beef and cook until softened, about 5-7 minutes. Add the minced garlic and cook for another minute until fragrant.
Step 3: Stir in the chili powder, ground cumin, smoked paprika, dried oregano, and cayenne pepper (if using). Cook for 1-2 minutes, stirring constantly, to toast the spices and release their aromas.
Step 4: Transfer the browned beef and onion mixture to a large slow cooker (6-quart or larger).
Step 5: Add the diced tomatoes (undrained), crushed tomatoes, tomato paste, rinsed and drained kidney beans, rinsed and drained pinto beans, diced green chiles (undrained), beef broth, brown sugar (or chocolate), and bay leaf to the slow cooker.
Step 6: Stir all ingredients together well to combine. Season with salt and black pepper to taste.
Step 7: Cover the slow cooker and cook on Low for 6-8 hours or on High for 3-4 hours, or until the chili is heated through and the flavors have melded.
Step 8: Remove the bay leaf before serving. Taste and adjust seasonings one last time if needed.
Step 9: Ladle the hearty chili into bowls and serve hot with your favorite toppings like shredded cheese, sour cream, green onions, and fresh cilantro. Enjoy your homemade slow cooker chili recipe!