In a dry skillet, toast the sesame seeds until golden brown, then set them aside.
In the same skillet, toast the ancho and guajillo chiles for a minute or two until they darken a bit and become aromatic, making sure they do not burn.
Place chiles in a bowl and add boiling water to cover. Let them soak until softened, about 30 minutes.
Drain the chiles, saving the soaking liquid, and put them into a blender with the toasted sesame seeds, almonds, raisins, chicken broth, chocolate, cinnamon stick, cumin, oregano, sugar, and olive oil. Blend until smooth.
Transfer the blended sauce into a large saucepan over medium heat and bring to a simmer. Add some reserved chile soaking liquid as needed to reach desired consistency.
Cook, stirring occasionally, for about 2 hours until thickened and flavors are well combined. If the sauce becomes too thick, thin it with a bit more chicken broth.
Season with salt to taste. Serve over your desired dish.