Endive (chicory). I love this stuff. The leaves are wonderfully bitter in a salad and are a good scoop for dips. Cooked, it is yummy - much sweeter. I simply halve them and cut out the bitter heart then place them in a pan loaded with butter on a medium heat. Flip and cook the other side and boom!
You can also cook them a bit less and then finish off in the oven in a variety of ways - with stock and herbs, gratin style with cheese, wrapped in parma ham and then covered with a cheese sauce (cheese and creme fraiche). They are underused IMO and a great things to have when they are plentiful in the winter.