Place the sesame seeds in a small heavy skillet over medium heat. Cook, stirring constantly, shaking the skillet, just until you see them starting to turn golden. Scrape the seeds out into a small bowl to stop the cooking and set aside.
Grate the chocolate coarsely on a straight-sided grater, or break or chop into small pieces. Set aside.
Crush the bread to fine crumbs or grind in a food processor. You should have about 1 cup. Set aside.
Wash and griddle-dry the chiles. Place in a bowl as they are done and cover generously with boiling water. Let soak for at least 20 minutes.
Meanwhile, grind the canela, cloves, and peppercorns together in an electric coffee or spice grinder or with a mortar and pestle. Set aside.
Drain the soaked chiles and reserve. In a medium-size skillet, heat half the lard over medium heat until rippling. Add the ground spices and cook, stirring, just until fragrant, 1-2 minutes. Add the onion, garlic, tomatoes, plantain, thyme, oregano, sesame seeds, raisins, and almonds. Cook, uncovered, stirring frequently, for 15 minutes.
Let the cooked mixture cool for 10 minutes, then place half the mixture in a blender with 1 cup chicken or pork stock and half the drained chiles. Process to a smooth purée (about 3 minutes on high). Repeat with the remaining sauce mixture, another 1 cup stock, and the remaining chiles.
In a large Dutch oven or deep skillet, heat the remaining lard over medium-high heat until rippling. Add the puréed mixture, stirring well to prevent splattering. Stir in the remaining stock, a little at a time. Cook, covered, for 15-20 minutes, stirring frequently, until the chiles lose the raw edge of their flavor. Stir in the bread crumbs and cook, stirring frequently, until the mixture is lightly thickened, about 10 minutes. Stir in the chocolate and cook, stirring constantly, until it is well dissolved. Add the salt.
Stir in the shredded meat. Cook, partly covered, stirring occasionally, just until heated through, 7-10 minutes. Taste for seasoning and add another pinch or two of salt if desired.