Add the bacon pieces to a large Dutch oven and place over medium heat, stirring occasionally so they brown evenly and become crisp, about 8-10 minutes. Remove with a slotted spatula to a plate lined with paper towels. Pour out the fat until there's 2 tablespoons left in the pot.
Add the onions to the bacon fat and sprinkle with the salt (not too much as the bacon fat is already salty). Stir occasionally until the onions are soft, about 5-8 minutes.
Add the tomato paste and stir it around until it darkens in color, about 2-4 minutes.
Add the chili powder, cumin, smoked paprika and cayenne and stir for 30 seconds. Scoot the spiced onions to the outer edge of the pan.
Add the ground beef, flipping and stirring occasionally, until browned, about 10-15 minutes.
When the meat is mostly brown, add 1 cup of the broth and scrape up the bottom of the pot to get all the flavorful brown bits. Stir in the rest of the broth, the diced tomatoes, cocoa/cacao powder, Worcestershire, molasses, espresso powder and liquid smoke, if using. Turn up the heat to bring the chili to a boil, then reduce the heat to medium low and simmer for at least 30 minutes (although 1 hour is great and 2 hours would be fantastic).
Stir in the bacon pieces and taste. If it needs more salt, start with 1/2 teaspoon and taste before adding more. Like almost any chili, this is best made at least one day in advance to let the flavors deepen.