If you don't mind a mustardy kick to your greens, Warty Cabbage, better known as Turkish Rocket (Bunias orientalis), is a great perennial vegetable.
Once installed, it is a wonderfully self-sufficient plant, seemingly unbothered by pests or drought, but you might want to remove the flowering stems before the seeds form as in the right spot it is a keen self-seeder.
I picked some of the young leaves yesterday:
Turkish Rocket in April
Variation in the leaf shape
and set about deciding what to do with it.
A few reports describe the young leaves as mild. Mine certainly aren't, they give quite a punch. I rather like the flavour though and go back for more! After nibbling some raw leaves I blanched some in boiling water as advised for bitter greens and tasted the flavour after 1, 2, 3, 5 and 10 minute soaking times. They became just a little milder over time I would say.
I then followed Turabi Effendi's advice from his collection of Turkish recipes as relayed by William Woys Weaver here. (I've learnt a lot from William Woys Weaver's articles - and have also just discovered he has some videos on You Tube. You can see him here talking about perennial salad greens and suggesting adding salad burnet to complement freshly cooked peas). So, I boiled some leaves in tomato juice with some fried onions and salt. A good taste.
Cooked with onions in tomato juice
Mr Weaver mentions that it is a Central European habit to mix the chopped greens with sour cream and minced dill or fennel. I didn't have any sour cream so I tried the leaves with yoghurt and chopped bronze fennel.
Turkish rocket and bronze fennel
With yoghurt and fennel
That made a really interesting flavour combination and a very delicious lunch alongside some leftover lentil stew on toast! It would be nice with some chopped cucumber in the yoghurt too.
I have had to delve a bit deeper to discover what else to do with warty cabbage (warty because of little bumps on the flower stems which are a useful identification clue). Here are the best of my gleanings.....
Stephen Barstow has a comprehensive Bunias orientalis entry in his book, "Around the World in Eighty Plants," plus a fascinating account on his website of three Thai women foraging for it in Oslo and talking about how they cook it. Here you can watch Jonathan Bates harvesting and cooking Turkish rocket 'broccolis' (4.26 minutes in). And to eat the stems, "just chew - it is delicious" - (from a translation of this site) and you can take some stems home and fry them in batter too. The flowers and the root are also edible.
All in all - just eat it!
N.B. I sell a range of perennial vegetable plants on my website.