Season chicken pieces with salt and pepper.
De-seed the guajillo chiles and toast on a griddle or a comal. The chiles should be blistered with a light char. Set aside.
In a large stock pot on medium, heat the oil. Once the oil is hot carefully place the seasoned chicken in pan with the skin side down. Sear the chicken on both sides until golden brown, carefully take the chicken out of the pot, and set aside.
In the same pot, add the onions and garlic, turn the heat to low, and cook until translucent and slightly caramelized.
While the vegetables are caramelizing, toast the sesame seeds, cumin, and pumpkin seeds until golden brown. Set aside.
Once the onions and garlic are caramelized, add the toasted chiles, seeds and cumin, cloves, and peppercorns to the pot.
Cover with water until the chiles are fully submerged. Bring to a boil and then take it down to a simmer. Cook until the chiles are tender and ready to fall apart.
Let sit for a few minutes to cool and then in a large blender, place all of the chiles, seeds, spices, and vegetables in the blender, and purée until smooth adding the liquid from the pot to help with the pureeing process. Carefully push the purée through a fine mesh strainer. Set aside the smooth mole and discard anything left in the strainer.
Place the chicken back into stock pot; add the chicken stock and mole. Simmer and reduce for about 45-60 minutes. When finished the mole should be a bright reddish-orange color with a smooth consistency that should slide down the backside of a spoon, and the chicken should be fork-tender and cooked through.
When ready to eat, place in bowl over your favorite rice and garnish with toasted sesame seeds. Serve with a side of warm tortillas. Buen Provecho!