Originally a Portuguese dish, Caldo Verde calls for collard greens. It also calls for using water instead of chicken stock. However, since I am not a fan of the bitterness of collard greens, I use fresh spinach instead; and I also like to cook with vegetable or chicken stock instead of just water. I find that the stock adds another layer of flavor. Here is my version of Caldo Verde.
Heat the oil in a large pot over medium-heat, add the onions and garlic and cook until onions are soft (for about 10 minutes).
Add the potatoes, cook quickly for a couple of minutes.
Add the stock and salt (starting with 1 teaspoon of salt and adding the rest if necessary to suit your taste).
Bring it to a boil, cover and reduce to a simmer. Cook until potatoes for about 30 minutes. Add the sausage and cook a few more minutes until the sausage is hot and the potatoes are fork tender.
I prefer my potatoes chunky in my soup. However, if you want a thicker soup, blend the soup by using an immersion blender directly in the pot or you can put the soup in batches into a blender and blend it. Add more chicken stock if you think it's too thick.
Taste the soup and adjust salt if necessary, add fresh pepper to taste.
Place a handful of spinach on the bottom of each bowl and pour soup over the spinach. Make sure the soup is extremely hot, as it will flash cook the greens.