Begin by taking a large pot and adding the chicken and peppercorns to it. Add enough water to cover the ingredients and season with salt. Bring the water to a simmer over low heat and allow it to cook until the meat becomes tender. This should take you about 40 minutes. Place the chicken on a plate and keep the cooking liquid separate.
Now, take the sesame seeds and toast them in a dry skillet over medium heat. Toast until they turn golden. This should take you approximately 5 minutes. Take out 2 tablespoons for garnishing at the end and shift the rest to a blender.
Next, toast the cloves, cinnamon stick, anise seeds and coriander seeds in the same skillet for about 3 minutes. Transfer it to the blender.
Get rid of the stems and seeds of the chile peppers. Again, in the same skillet, add 4 tablespoons of canola oil and heat it over medium heat. Throw in the chiles and fry for about 2 minutes. Make sure they are lightly toasted. Shift to a bowl, add enough hot water to cover the chiles and keep them aside to soak for about 30 minutes.
In the meantime, take the skillet again and add oil to it. Throw in the raisins, almonds, pumpkin seeds and tortilla pieces and stir until the seeds and tortillas are golden brown. This should take about 2 minutes.
Once done, transfer all these ingredients to the blender, along with the oil from the skillet. Now, add the softened chiles and puree (adding 2 to 3 cups of the liquid to prepare a smooth sauce).
Now, heat the residual oil in a large pot over a medium-high flame. Pour the chile sauce in and stir until it has thickened. It should take 5 to 6 minutes. Reduce the heat to low and pour in the 4 cups of the reserved chicken cooking liquid, allowing the sauce to thicken. Let it cook for about 20 minutes. Throw in the chocolate and simmer. Make sure to stir often until the chocolate dissolves and the sauce reduces. Next, add the sugar and salt to taste.
Lastly, add the chicken pieces to the sauce and let them warm over low heat. Top the dish off with the set-aside sesame seeds.