Their large, smooth leaves, deep green in color, don't form a head, but grow outward from a central axis.
Collards are a cabbagelike green with smooth leaves and mild taste.
Bring a large pot of salted water to boil over high heat. Add collard leaves and boil under tender, about 5 mins. Drain, refresh under cold running water, and drain again well. Bring to a simmer and simmer until water evaporates and onion is softened, about 5 mins. Add tomato and simmer 10 mins.