Place the ground beef, Italian sausage, and salt in a large bowl. Mix the baking soda with 1 tablespoon of water and pour over the meat. Using your hands, mix everything until evenly combined, then set aside to rest at room temperature for 20 minutes.
In the meantime, chop the yellow onion, bell pepper, and jalapeño (keep the seeds for extra heat, if desired).
Heat 2 tablespoons of neutral oil in a large pot over medium heat. Once hot, add the ground meat to the pot in quarter-sized pieces. You may need to do this step in batches, since overcrowding the pan will prevent a sear from forming.
Let the meat develop a golden-brown crust on the bottom before stirring, about 1-2 minutes. Once browned, use a wooden spoon to flip and break the meat into smaller pieces. Cook until the beef is browned all over—it does not have to be fully cooked through, since the meat will finish as the chili simmers.
Using a slotted spoon, transfer the meat to a dish lined with paper towels. Set aside to drain.
To the same pot, add the onions, red bell pepper, and jalapeño with a pinch of salt. Add more oil, if needed. Stir frequently over medium heat until the onions are softened and translucent, 5 minutes.
Add in the minced garlic and cook for 1 minute more. Sprinkle over the chili powder, cumin, smoked paprika, oregano, coriander, and cayenne (if using). Stir frequently for 1-2 minutes until fragrant, being careful not to let the spices burn.
Mix in the tomato paste until well combined and cook for 2-3 minutes, stirring constantly, until the paste takes on a darker color and begins to stick to the bottom of the pan.
Carefully pour in the crushed tomatoes, fire-roasted tomatoes, and beef broth, scraping the bottom of the pot to ensure everything is combined. Stir in the kidney beans and pinto beans along with their liquid, then add the brown sugar and cocoa powder (if using). Bring to a boil.
Reduce the heat to low and simmer, covered, for 2 hours, stirring occasionally. Taste and adjust for seasoning, if necessary. For a thinner chili, stir in more beef broth. For a thicker consistency, let the chili simmer, uncovered, until the desired consistency is reached. Serve hot with shredded cheese, sour cream, lime wedges, and Fritos or cornbread.