Soak the beans overnight, or for 8-10 hours. Drain and rinse them.
Heat the oil over medium heat in a large soup or stock pot. When the oil is shimmering, add the onions. Cook for 5-7 minutes, or until the onions are tender and clear. Add the garlic and cook for another 2 minutes, stirring constantly.
Add the beans, 7 cups water, and bay leaves to the pot. Bring the beans to a boil, then reduce the heat to low. Cover and simmer for 45 minutes.
Remove the bay leaves. Add the salt and kale to the pot (you may need to add the kale gradually, stirring as you go, in order to wilt it down and fit all of it). If the mixture you have is too thick, add an extra cup or more of water: you want the beans and kale to be less soupy than a soup, but still pretty soupy.
Cover the pot again and continue to simmer the beans and kale for another 30 minutes, or until the kale is meltingly soft. Taste the beans and add salt as needed; then, add freshly ground black pepper and a splash or two of red wine vinegar to taste. Serve. (The mixture is even tastier as the leftovers sit.)