Warm the olive oil in a large Dutch oven or soup pot over medium heat. Add the sliced linguiça or other fully cooked smoked sausage and cook, stirring occasionally, until lightly browned. Transfer the sausage to a clean plate, leaving the flavorful drippings in the pot.

Add the onion to the pot and cook until softened, stirring often. Add the garlic and stir just until fragrant so it does not brown.

Add the potatoes, broth, salt, and pepper. Bring the liquid to a boil, then reduce the heat to maintain a gentle simmer. Cover partially and cook until the potatoes are very tender and break apart easily when pressed with a spoon.

Turn off the heat. Use an immersion blender to carefully blend the soup in the pot until mostly smooth. For a little texture, leave a few small potato pieces. If using a countertop blender, blend in small batches, filling the blender no more than halfway and venting the lid carefully to allow steam to escape, then return the soup to the pot.

Return the soup to low heat. Stir in the kale ribbons and the browned sausage. Cook just until the kale is tender but still bright green. Stir in the red wine vinegar, if using, then taste and adjust the salt and pepper. Ladle into bowls and finish with a small drizzle of olive oil if desired.