In a Dutch oven, heat the olive oil over medium heat. Add the onion and saute until tender and translucent, 7 to 8 minutes. Stir in the garlic and cook 1 minute. Add the broth, beans (do not drain) and kale. Bring to a low boil, reduce to a simmer, cover and cook until heated through, about 25 minutes.
Serve with sour cream, shredded cheese and diced avocado, if desired.