Set oven rack about 6 inches from the heat source and preheat the oven's broiler. Line a baking sheet with aluminum foil.
Cut the peppers in half from top to bottom. Place the peppers cut-sides down onto the prepared baking sheet.
Cook under the preheated broiler until the skin of the peppers has blackened and blistered, 5 to 8 minutes. Place the blackened peppers into a bowl and tightly seal with plastic wrap. Allow the peppers to steam as they cool, about 20 minutes. Remove and discard excess blackened skin and stems. Tear peppers with your hands and place in a bowl.
Cut the top off of each tomato around the stem. Scoop seeds and pulp out of each tomato and squeeze into a bowl to create a thick tomato 'juice'. Chop tomatoes and place in a separate bowl.
Heat corn oil and olive oil together in a large pot over medium heat. Cook and stir black pepper, paprika, cloves, cinnamon, and cayenne pepper in hot oil until fragrant, about 30 seconds.
Stir onion and garlic into hot spiced oil; cook and stir until onion is softened, about 5 minutes. Pour tomato 'juice' into the pot and bring mixture to a boil while scraping the browned bits of food off of the bottom of the pot with a wooden spoon. Add chopped tomatoes, chicken broth, raisins, and brown sugar. Bring to a simmer.
Reduce heat to low and add the chocolate; stir until chocolate melts. Add roasted peppers and stir. Bring sauce to a simmer and cook until flavors blend, at least 1 hour.
Pour sauce into a blender no more than half full. Cover and hold lid down; pulse a few times before leaving on to blend. Puree in batches until smooth. Return sauce to the pot and season with salt.
Tips & Tricks
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To roast the peppers over an open flame, place a small bit of oil in a bowl, roll your peppers in this and roast them over a fire. I like to roast them over my gas oven. It makes the house smell like memories of some Mexican small town or beach resort I have been to. Once the peppers are blackened place them in a paper bag, close it up, they steam up and are easier to clean/peal. The longer you let them sit the easier they are to peel.
You can red pepper flakes for the cayenne pepper, pitted prunes for the raisins, and semisweet chocolate chips or 2 tablespoons cocoa powder for the Mexican chocolate.