1. On a baking sheet, place costeño, guajillo, and ancho chiles and bake at 356 F for 5 minutes.
2. In a blender, combine chiles, raisins, almonds, sesame seeds, garlic, onion, tomato, cloves, allspice berries, cinnamon, plantain, tortilla, chicken broth, salt, and sugar, and blend for 5 minutes. Set aside.
3. In a clay pot, heat lard. Pour mole negro into the clay pot and cook, stirring constantly, over medium heat for 25 minutes. Add Oaxacan chocolate and cook for 15 more minutes.
4. Add short ribs and cook for 15 more minutes.
5. Serve short ribs with mole negro with Mexican red rice on the side.