In a large saucepan, bring the chicken stock and ancho chiles to a boil. Lower the heat and simmer until the anchos are softened, about 10 minutes. Using a food processor, puree the anchos and stock.
While the chiles are working, in a large dutch oven or soup pot, heat the oil over medium-high heat until smoking. Add the bacon and cook until crisp, 2 to 3 minutes. Add the chicken and cook over high heat, breaking it up with a spoon, until browned, about 8 minutes. Lower the heat, add the yellow onion and garlic and cook until softened, about 5 minutes; season with pepper. Stir in the tomato paste for 1 minute.
Pour the ancho stock into the chili. Stir in the tomatoes, cocoa, paprika, coriander and cinnamon and simmer for a few minutes; season with salt if necessary. Serve in bowls and top with the cheese, sour cream, red onion and cilantro.
