I'm (fingers crossed) hoping that Itaunas might have some tips, but I'm looking for kale soup similar to the style that you get in New Bedford/Fall River. Normally I've found that in the East Cambridge restaurants, kale soup is usually a potato puree with very finely shredded kale, sometimes a bit of meat.
What I'm looking for (without having to head to Antonio's in NB) is a clear, red-tinged broth, big pieces of kale and linguica, maybe a bit of cubed potato or kidney beans.
You can definitely get that type of soup around here, but might need to experiment a bit to find the right one. The potato based one is "caldo verde," whereas a soup like Antonio's might be called sopa de legumes or something like that. If it has the kidney beans it might be called stone soup. One issue is some restaurants might make that into their vegetarian offering and leave off the linguica. Sunset definitely has a soup with the potatoes, linguica, some kale (I think its sopa a portugesa). I tend to get their sopa de alho, so haven't had it in a long time, but it didn't turn me off like their seafood soup. Portugalia has a sopa de legumes, but I think they might be guilty of dropping the linguica off but you could request it. (Most recently I have had their canja, which was decent, but not earth shattering. More consistent overall than Sunset.) I also know the chef at Guiseppe's in Medford was serving this soup for a while (they appear to be on vacation right now, so call before checking this one out). I'll try to think of one or two other ideas, but no solid rec.
the best kale soup I had was in Provincetown at Tip's for Topsn' on Bradford St. It is owned by locals and they make a mean soup. The bread was not so hot at all ( I am comparing it to the old Arturo bread place on Rte 6i n Truro back in the 80's which totally kicked ass!!) If they had the great bread, the soup would be worth the trip.
Cafe Polonia had a kale soup on the specials board this past winter, but it was not as you describe.