This makes a wonderful early Fall meal with some sliced apple and cheddar!
Cook onions in oil in an 8 quart pot over moderatley low heat, stirring occasionaly, until softened, 4-5 minutes. Add garlic and cook, stirring, for 1 minute. Add beans, broth, salt, pepper, bay, rosemary, and simmer, uncovered, for about 20 minutes.
While soup simmers, brown sausage (if using) in a heavy skillet over moderate heat. Then stir carrots into soup and simmer 5 minutes. Stir in kale and sausage and simmer uncovere, stirring occasionally, until kale is tender, 12-15 minutes. Season with salt and pepper.