A Portuguese recipe, called Caldo Verde (green broth).  Cabbage can substitute for the kale.

2 T olive oil
1 medium onion, chopped
2 cloves garlic, minced
3 large potatoes, diced
2 t dried thyme
6 c broth or water
6 to 8 c kale, rinsed, stemmed, and coarsely chopped
salt and pepper, to taste
1 cooked (garlic) sausage, sliced, optional
extra-virgin olive oil, optional

1. Heat the olive oil in a large soup pot over medium heat. Add onion and garlic, and sauté, stirring occasionally, until onion is softened, about 5 minutes, being careful not to brown the garlic. Add potatoes, stirring to coat with oil. Sprinkle with thyme.

2. Add broth and bring to the boil, then cover, reduce heat, and simmer for 10 minutes. Add kale and continue cooking another 15 minutes, until potatoes are soft and kale is tender. Season with salt and pepper.

3. In the soup pot, lightly mash the potatoes with a potato masher or the back of a wooden spoon (or not). If desired, serve with sliced  sausage that has been heated briefly in the soup and a splash of extra-virgin olive oil.