Scrub them, chop into 2 cm bits, and roast them in oil and a sprinkle of salt, with rosemary, bay or thyme. When they're done (they go so creamy they almost fall apart) serve them with a squeeze of lemon, rocket, toasted hazelnuts and chunks of hard goats cheese in a salad (thanks to River Cottage's Hugh Fearnley-Whittingstall for that recipe). My favourite is a slight amendment to that recipe, so that I melt the cheese (grated) and nuts into the lemony artichokes for the last 5 or so minutes of cooking so it becomes a kind of artichoke bake.
But, I have to warn you - these things have a bit of a kick - they might be really healthy, but boyo, they're not called 'fartichokes' for nothing! Adding asafoetida (you get it in Asian grocery stores) does help somewhat.
I've been teaching on a Permaculture Design Certificate, and, knowing we had rather a lot of these things in the ground, I asked if anyone on the course wanted some. About 6 people put up their hands, so the next morning, I took our 18 month old daughter out to help me harvest some.
Even knowing they're productive, I was still surprised at just how many we found... 5 and a half kilos... in about 3 square feet of soil!