Cut meat into 2-inch cubes and soak overnight in refrigerator. Next morning, discard water. In large pot, put meat cubes, add water and cook over medium heat till meat is tender. Set aside. Peel plantain, and cut into 3-inch pieces. Skin sweet potato, and cut into 3-inch cubes. Remove hard skin, seeds, and stringy portion from pumpkin, and cut into 3-inch cubes. In a large pot, heat oil and butter, sauté the onion, add celery, cinnamon sticks, allspice and cloves. Add water, meat, and cook for 10-minutes, then add the plantain, sweet potato and pumpkin. Cook over medium heat, until vegetables are done. If too watery, scoop out vegetables and continue cooking to reduce liquid to a heavy sauce. Return vegetables to sauce, stir lightly. Add sugar according to taste.