This is the dish that opens the great Christmas Day feast in Neapolitan households. It's called Minestra Maritata, or married soup, presumably because of the highly successful marriage of rich meat stock and slightly bitter greens. It's a beautiful dish--dark winter greens and clear amber broth--with origins that go back to the 16th century.
In days of yore, all sorts of animal parts were used to add substance to the broth for this soup, including pig's ears (lots of cartilage there to give body to the both) and guanciale, or cured pork cheeks. The modern version is simpler, with more familiar meats and a variety of greens that are not generally available in America--borage and chicory shoots, for instance. If you happen to have such things in your garden, by all means include them.
Slideshow: Warming Soup Recipes