Heat a large skillet over medium heat and toast the chiles, turning frequently, until very pliable and soft; do not allow to char. Remove from the skillet and transfer to a plate. Remove the stems and seeds and place in a saucepan. Add enough hot water to just cover and bring to a boil. Cover the pan, remove from the heat and allow chiles to soak until very soft and plumped, about 20 minutes. Strain in a fine mesh sieve over a bowl and reserve soaking liquid separately.
In a blender, combine the chiles, 2 tablespoons of the onion, 3/4 teaspoon of the garlic, 1 1/2 teaspoons salt, 1/2 teaspoon sugar, oregano, thyme, cinnamon, cumin, allspice, cloves, and vinegar and puree until smooth, adding a little of the chile soaking liquid (only as much as is needed) to enable the mixture to blend. The consistency should be thick but smooth. Cover and refrigerate until ready to use.
Trim the pork tenderloins of all silver skin and place in a re-sealable plastic food storage bag. Add 1/4 cup of the chili sauce and turn so that the tenderloins are both well coated with the sauce. Refrigerate for 45 minutes and up to 4 hours. Remove the meat from the refrigerator and allow to come to room temperature for 20 minutes.
Preheat the oven to 350 degrees F.
Heat a large skillet and, when hot add 2 tablespoons of the olive oil. When the oil is hot, sear the tenderloins until golden brown on all sides, about 4 minutes. Transfer to the oven and continue to cook until they reach an internal temperature of 145 degrees F, 10 to 12 minutes longer. Remove from the heat and set aside to rest for about 5 minutes before slicing to serve.
While the pork is roasting, make the sauce. In a medium saucepan heat the remaining tablespoon of olive oil until hot. Add the remaining 1/4 cup minced onion and remaining 1 1/2 tablespoons of garlic and cook, stirring, until soft, about 4 minutes. Add 1/4 cup plus 2 tablespoons more of the adobo sauce and cook, stirring, for 1 minute. Add the chicken broth and heavy cream and cook until sauce has reduced and is thick enough to coat the back of a spoon, 6 to 8 minutes. Add the chocolate and stir until melted. Season, to taste, with salt and serve immediately drizzled over the pork slices.