Brown the Meat: Heat olive oil in a large skillet over medium-high heat. Add the ground beef and onion. Cook, breaking up the meat with a wooden spoon, until the beef is no longer pink and the onions are translucent (about 5-7 minutes). Drain excess fat if desired, but leave about 1 tablespoon for flavor. Remove from heat and stir in the garlic, chili powder, smoked paprika, oregano, cumin, cayenne, salt, and pepper until well combined.
Combine Slow Cooker Ingredients: Transfer the beef mixture to your slow cooker. Add the black beans, kidney beans, crushed tomatoes, tomato paste, and beef broth. Stir everything together until smooth.
Cook on Low: Cover and cook on LOW for 6-8 hours or HIGH for 4-5 hours. The chili is done when it has thickened slightly and the flavors have melded. If you want a thicker consistency, remove the lid and cook on HIGH for the last 30 minutes.
Prepare Nachos: Preheat your broiler to high. Place tortilla chips in a single layer on baking sheets or in large oven-safe bowls. Ladle a generous amount of chili over each portion, ensuring some chips are covered. Sprinkle with shredded cheddar cheese and jalapeños if using.
Melt and Serve: Broil for 1-2 minutes until the cheese is bubbly and slightly browned at the edges. Watch closely to prevent burning! Remove from oven, garnish with fresh cilantro and a dollop of sour cream, and serve immediately while hot.
