I cook with it a lot. Kale is a form of cabbage - it comes in green and purple, as well as curly and flat leaf varieties. You may also see Dinosaur Kale, which is also known as Tuscan Kale or black kale.
Kale is "very high in beta carotene, vitamin K, vitamin C, lutein and reasonably rich in calcium." Fun trivia fact from Wikipedia - "During World War II, the cultivation of kale in the U.K. was encouraged by the Dig for Victory
campaign. The vegetable was easy to grow and provided important
nutrients to supplement those missing from a normal diet because of rationing."
Since still had some leftover lentil cakes, I decided to make a quick kale side to go with them. I sauteed some shallots and garlic in olive oil, and then added a few dollops of concentrated tomato paste. I then added a head of flat leaf kale, ribs removed and leaves coarsely torn, and two cups of vegan bouillon. I put the lid on and let everything cook down, seasoning it with black pepper and red pepper flakes before removing it from the pan. The whole process took about 15 minutes total.
I liked the flavors, especially the kick of the red pepper flakes, but if I do this again, I'd change two things. First, I'd use a lot less liquid - it essentially became a quick soup. Second, while the kale cooked down quite a bit, I think I'd chop it up more to make it more manageable to eat.