Caldo Verde with Beef Shank and Sausage

In a large pot, heat the olive oil. Season the beef shank with salt and black pepper and add it to the pot. Cook over moderately high heat, turning, until browned all over, about 8 minutes. Transfer to a plate. Add the onion, bay leaf and a generous pinch each of salt and black pepper to the pot and cook, stirring occasionally, until the onion is softened, about 5 minutes. Add the garlic and crushed red pepper and cook, stirring, until fragrant, about 2 minutes. Add the stock, beans and 2 cups of water and bring to a boil. Return the beef shank to the pot. Cover and cook over moderately low heat until the beef and beans are tender, about 2 hours and 30 minutes. Add the potatoes to the pot and simmer uncovered, stirring occasionally, until tender, about 30 minutes. Using tongs, transfer the beef shank to a plate. Add the kale to the pot and cook, stirring occasionally, until wilted, about 10 minutes. Pick out and discard the bay leaf. Using 2 forks, shred the beef into bite-size pieces. Discard the bone and any gristle. Add the beef and sausage to the pot and simmer for 5 minutes. Stir in the 2 tablespoons of vinegar and season with salt and black pepper. Ladle into bowls and serve, passing more vinegar at the table.