That is definitely a brassica -- which means it could be any sort of cabbage or even broccoli or cauliflower. My guess is that it is either a red heading cabbage or a variety of broccoli. Why not let it go to seed then plant some of them and ssee what you get? Whatever it is will be edible, so you can't lose.
I've got to say it looks a lot like my russian kale that's bolted after overwintering.
"Instead of Pay It Forward I prefer Plant It Forward" ~Howard Story / "God has cared for these trees, saved them from drought, disease, avalanches, and a thousand tempests and floods. But he cannot save them from fools." ~John Muir