I don't have much to say about this recipe other than it's delicious and it's ridiculously simple to execute, which may mean that this will be the shortest Food Lab post EVER. Fancy that!
The trick to this recipe is to start with a crazy flavorful ingredient—Italian sausage—add to it a few other crazy flavorful aromatics—garlic, rosemary, and lemon zest—then cook it all down with a couple of ingredients that just love sopping up flavor—dried beans and kale.
Ok, there are a few more tricks than that, like soaking the beans in salted water overnight in order to improve their texture (the salt weakens the structure of the beans' skins, which allows it them tenderize more effectively when simmering later on), or adding the rosemary and lemon zest in two stages: once at the beginning to flavor the broth, and once just before serving to give your soup a punch of flavor at the end. But really, it's simple. I swear.
The last key to good flavor here? Really, really good olive oil drizzled over the top at the end. Break out the fancy stuff. Now is the time.