Take whatever greens you are using and stack several leaves on top of each other. Starting at the wide side, roll the stack up into a tight cylinder. Slice across the cylinder with a very sharp knife to make thin, hairlike shreds. Repeat with remaining leaves. Set aside shredded greens.

Heat 1 tablespoon olive oil in a large kettle over medium high heat. Add sausage slices and fry until lightly colored and fat is rendered, about 10 minutes. Remove from pot with slotted spoon and reserve. Add remaining tablespoon oil to pot, then add onions and salt and pepper. Stir well, then cook, stirring occasionally, until onions are softened, 5 minutes. Add the garlic, stir, and cook one minute until its aroma is released. Add the potatoes, turn the heat to medium high, and saute 3 to 5 minutes until onions and potatoes begin to color. Add the water, cover, and simmer over low heat until potatoes can be mashed easily against side of pot with a wooden spoon, about 25 minutes. When potatoes are soft, turn off the heat and use a potato masher to thoroughly crush and blend. Add the sausage, turn the heat on to medium, and simmer 5 minutes to bring the flavors together. Stir in the greens and cook 5 minutes until bright green and tender. Taste, adjust seasoning, and serve.

This soup, literally Green Soup, could be called the national dish of Portugal. It is traditionally made with a type of flat green cabbage called couve gallego.

The method of slicing leaves like this is called a chiffonade in the French lexicon. Important to get them thin enough that they will cook quickly.