Finely dice the onion into approximately 1/4-inch pieces, mince the garlic, and chop the red bell pepper into roughly 1/2-inch pieces. Keeping the vegetables relatively uniform in size helps them cook at an even rate.
Warm the olive oil in a large, heavy-bottomed pot over medium heat until shimmering. Add the onion and cook for 3–4 minutes, stirring occasionally, until softened and translucent.
Stir in the minced garlic and chopped bell pepper. Cook for another 2 minutes while stirring regularly, allowing the garlic to become fragrant without letting it brown.
Add the ground beef, or beef-and-pork blend, to the pot. Break the meat into small pieces with a wooden spoon as it cooks.
Increase the heat to medium-high and cook for 5–7 minutes, stirring frequently, until no pink remains and the meat develops light browning.
Carefully tilt the pot so that excess rendered fat collects on one side. Spoon away and discard the surplus fat.
Sprinkle in the salt, black pepper, smoked paprika, cumin, chili powder, and dried oregano. Stir continuously for approximately 1 minute so the spices warm in the residual fat and release their aroma.
Add the tomato paste and Worcestershire sauce to the seasoned meat. Stir continuously for about 1 minute, allowing the tomato paste to cook briefly against the hot surface of the pot and develop a richer flavor.
Pour in the crushed tomatoes and beef broth. Stir thoroughly until the meat, vegetables, and liquid ingredients are evenly incorporated.
Stir in the rinsed and drained kidney beans. Add the optional sugar at this stage if using it.
Bring the chili to a gentle simmer over medium heat. Reduce the heat to low and leave the pot uncovered. Cook for 30 minutes, stirring from time to time as the sauce reduces and the seasonings meld together.
After the 30-minute simmer, stir in the dark chocolate if using. Continue stirring for about 1 minute, or until the chocolate has completely melted into the sauce.
Remove the pot from the heat and taste the chili. Adjust with additional salt, black pepper, or the existing spices as necessary, keeping the overall seasoning balanced.
Spoon the hot chili into serving bowls. Finish each portion with chopped cilantro or flat-leaf parsley, a spoonful of sour cream or plain Greek yogurt, and shredded cheddar cheese.
Serve with steamed white rice or tortilla chips, either alongside the chili or added as a topping for extra texture.