Heat olive oil in a large pot over medium heat. Add onion and cook until softened, about 5 minutes. Add garlic and cook for 1 minute more.
Add vegetable broth, potatoes, cannellini beans, fennel seeds, and red pepper flakes to the pot. Bring to a boil, then reduce heat and simmer for 20 minutes, or until potatoes are tender.
Add kale and cook for 5 minutes more, or until wilted. Season with salt and pepper to taste.