Heat the olive oil in a large skillet over medium-high heat. Add the diced onion and sauté until translucent, about 5 minutes. Add the minced garlic and cook for another minute until fragrant. Add the ground beef and cook, breaking it up with a spoon, until fully browned and no longer pink. Drain any excess fat.
Transfer the browned beef mixture to your slow cooker. Add the light brown sugar, chili powder, ground cumin, ground cinnamon, crushed tomatoes, tomato paste, salt, black pepper, red pepper flakes, cocoa powder, and beef broth. Stir to combine.
Stir in the rinsed and drained kidney beans, cannellini beans, and sweet corn.
Cover and cook on low for 6 to 8 hours, or on high for 3 to 4 hours.
Taste your chili and adjust salt, pepper, or chili powder to your preference. For thicker chili, remove the lid and cook on high for an additional 30 minutes.
Spoon the chili into bowls and garnish with your favorite toppings like shredded cheese, sour cream, chopped green onions, or fresh cilantro. Serve with cornbread or tortilla chips.