Add onion, carrot, and potato to pot, lower heat to medium, and cook, stirring occasionally, until vegetables begin to soften, about 5 minutes. Add garlic and rosemary, and cook, stirring, until fragrant, about 30 seconds. Add beans, tomatoes, and reserved broth, bring to a simmer, and cook for 10 minutes, skimming as needed. Add kale and reserved sausage, and simmer for 5 minutes. Season with salt and pepper to taste.