Preheat the oven to 325 degrees F.
Arrange the short ribs on a large sheet of foil. Sprinkle all over with 1 teaspoon salt and 1 teaspoon pepper.
Bring the New Mexico chiles, ancho chiles and 1 1/2 cups water to a simmer in a medium saucepan over high heat. Cover, reduce the heat to medium-low and simmer until the chiles are just tender, 5 to 6 minutes. Transfer the mixture to a blender. Holding the top on firmly, blend until the chile puree is smooth.
Heat the oil in a large pot over medium-high heat. Add the short ribs in batches and brown on all sides, 5 to 6 minutes per batch, transferring the short ribs to a bowl each time.
Add the garlic and red onions to the drippings in the pot. Saute until the onions soften, about 5 minutes. Mix in the cumin and oregano. Add the chile puree from the blender, the broth, agave, and espresso; stir to blend. Return the short ribs and any juices from the bowl to the pot; stir to coat. Bring to a simmer. Cover and place the pot in the oven. Braise until the ribs are very tender, about 2 hours 30 minutes.
Tilt the pot. Spoon off and discard any fat that rises to the surface and pools at the lower end. Using tongs, transfer the ribs and any loose bones to a rimmed baking sheet. Carefully cut the membrane off each piece of meat (try to cut away only the membrane and not any meat). Discard the membranes and all bones. Cut the meat into small (scant 1/2-inch) cubes. Return the meat to the sauce in the pot. Mix in the black beans. Season the chili with about 1/4 teaspoon each of salt and pepper. If desired, add the adobo sauce by teaspoonfuls to increase the spiciness. Transfer the chili to a large bowl. Sprinkle with the green onions.
Spoon the Creamy Corn Polenta into deep bowls. Ladle chili over. Sprinkle generously with chocolate. Serve with the garnishes.
Bring the broth, 2 1/2 cups water, butter and 1 teaspoon salt to a boil in a heavy, large saucepan over high heat. Gradually whisk in the polenta. Continue to whisk until the polenta begins to thicken, 2 to 3 minutes. Reduce the heat to low. Cover and cook until the polenta is very thick and tender, stirring often with a flat-bottom spoon or heatproof rubber spatula to prevent sticking or burning, about 20 minutes. Blend the corn in a mini processor until a coarse puree forms. Stir the corn puree into the polenta. Season with more salt if desired.