Caldo verde, Portuguese soup

I came across a reference to Caldo Verde recently, and since I liked what I was reading, decided to give it a try.  This seems to be another of those traditional soups where there are as many variants as there are cooks, but here's what seems to be working for us:

Caldo Verde

12 oz linguica sausage, sliced
Olive oil
Onion, chopped
3 cloves of garlic, minced
Red pepper flakes
Salt and pepper
3 - 4 Yukon Gold potatoes, chopped to 3/4 inch pieces
4 c chicken broth
2 - 4 c water
1 lb kale (or collards) chopped
2 t white vinegar

Brown the linguica in a bit of olive oil in a Dutch oven; remove from pot and set aside.  Over medium heat, cook the onions and garlic with a dash of red pepper flakes, salt, and pepper.  Cook until translucent, a few minutes.

Add the potatoes, broth, and 2 c water and bring to a boil.  Reduce heat to medium low and simmer until potatoes are tender, about 10 minutes.  Dip out about 2 c of potato and broth into a large glass measuring cup.  Add about 3 T olive oil to the mix, and blend really well with an immersion blender.  Set aside.

Add the greens and the linguica to the pot and simmer for about 10 minutes.  Add up to 2 c more water, only as needed.  Give the blended portion another blast, and add it to the soup, along with the vinegar.