Put the turkey, onion, celery, cilantro sprigs, cloves, allspice, star anise, peppercorns and 1 teaspoon salt in a large pot; add cold water to cover. Bring to a simmer over medium-high heat, then reduce the heat to medium low and simmer until very tender, about 1 hour, 30 minutes.
Remove the turkey with tongs and transfer to a plate to cool slightly. Strain the broth through a fine-mesh sieve into a large measuring cup or bowl. You should have about 8 cups broth; if you have more, simmer until reduced to 8 cups. Skim the fat off the surface.
Remove the turkey skin; refrigerate the meat until ready to use. (The turkey and broth can be made 1 day ahead; cover and refrigerate.)
Make the mole: Preheat the broiler.
Put the tomatillos, tomatoes, garlic and onion on a rimmed baking sheet. Broil, turning, until charred, about 10 minutes.
Transfer to a bowl to cool.
Remove the skins from the tomatoes and garlic.
Heat 1/4 cup vegetable oil in a large skillet over medium-high heat. Fry the ancho and pasilla chiles in batches, turning, until softened, 30 to 45 seconds; transfer to a bowl. Fry the tortilla in the hot oil, turning, until browned, 4 minutes; add to the bowl with the chiles. Cover with water and soak 30 minutes, then drain.
Add the chiles and tortilla to the bowl with the tomatillo mixture and set aside.
Meanwhile, discard the oil in the skillet and wipe clean.
Heat another 1/4 cup vegetable oil in the same skillet over medium-high heat.
Add the almonds and fry, stirring, until golden, 3 minutes.
Add the raisins and stir until plump, 30 seconds; transfer to a bowl using a slotted spoon.
Add the pepitas and fry, stirring, until they begin to pop, 2 minutes; transfer to the bowl with the almonds.
Discard the oil in the skillet and wipe clean.
Heat the skillet over medium heat.
Add the sesame seeds and toast, stirring, until golden, about 3 minutes; transfer to a clean bowl to cool.
Add 1 heaping tablespoon of the ancho chile seeds, the allspice, peppercorns, cloves, star anise and cinnamon stick to the skillet and toast, stirring, 2 minutes; transfer to the bowl with the sesame seeds and let cool. Grind the sesame-spice mixture in a spice grinder to make a fine powder.
Put the fried almonds, raisins, pepitas, sesame-spice powder, 1/4 teaspoon salt and 2 cups of the reserved turkey broth in a blender and blend until smooth; transfer to a bowl. Working in batches, blend the broiled vegetables, fried chiles and tortilla, 1 teaspoon salt and 2 cups turkey broth until smooth.
Heat the remaining 1/4 cup vegetable oil in a large Dutch oven over medium-high heat.
Add the pureed chile mixture and cook, stirring frequently, until slightly thickened, about 5 minutes (be careful-the mixture will spatter). Stir in the ground almond mixture and 2 cups turkey broth; bring to a simmer over medium-low heat. Stir in the chocolate until melted.
Add the turkey thighs and simmer until heated through, about 30 minutes. The mole should be the consistency of gravy; thin with more broth, if necessary. Season with salt.
