Pour 2 cans of the black beans into a food processor or blender, along with the can of tomatoes. Puree until smooth. Set aside.
Melt butter in a soup pot over medium heat. Add the onion and garlic, and season with salt and pepper. Cook and stir until the onion is softened. Stir in the bean puree, remaining can of beans, beef broth, pumpkin puree, and sherry vinegar. Mix until well blended, then simmer for about 25 minutes, or until thick enough to coat the back of a metal spoon. Stir in the ham, and heat through before serving.
