Preheat the slow cooker if necessary; see the manufacturer's instructions. Put the chorizo, onion and haricot beans into the slow cooker pot, add the tomatoes, garlic and rosemary and mix together. Arrange the frankfurters and olives, if using, on the top.
Mix the boiling stock with the tomato purée and a little salt and pepper, then pour into the slow cooker pot. Cover with the lid and cook on high for 4–5 hours. Stir the beans, then spoon into bowls. Serve with hot peppered foccacia or garlic bread and a green leafy salad.