Cook the sausage: Heat the olive oil in a large sauté pan over medium heat and add the bulk sausage; if you can't find bulk sausage, remove the casings on the links. Cook for 3 to 4 minutes, until the sausage is mostly cooked. Remove with a slotted spoon to a bowl.
Cook the onions and garlic: Add the onion slices to the pan and increase the heat to high. Cook until the edges of the onions brown, about 3 to 4 minutes. Add the garlic and cook for another minute. Return the sausage to the pan with the onions.
Add the kale, salt, chicken stock: Add the kale, sprinkle salt over everything, then add the chicken stock. Cover the pan, lower the heat to medium and cook for 2 minutes.
Add the beans: Uncover, mix everything well (the kale will have cooked down by now) and add the beans. Cover the pot again and lower the heat to low. Cook another 5 minutes, then turn off the heat. Let stand 5 minutes, sprinkle with a splash of vinegar and serve.
Note. We used curly kale for this recipe, but you could use any kale, as well as chard, turnip greens, beet greens, or collards. A splash of vinegar (sherry, red wine, cider) is a nice touch right at the end of cooking.
