Isn't it great that just when the weather gets cold, there are lots of things in the garden to make soup from. Jerusalem artichokes are one of our favourites, and they're one of the easiest things to grow.
To make the soup, chop an onion and soften it in oil or butter. Add a couple of heaped handfuls of scrubbed artichokes, and enough vegetable stock to cover the mixture. I don't know if it makes much difference, but I cut the artichokes into inch-long chunks to speed things up. Once the artichokes are soft (they almost dissolve) add a handful of chopped parsley and blitz the mixture with one of those whizzers - or a potato masher would probably do the job. If it's too thick, add a bit more water, or maybe some cream if you're really pushing the boat out.
A word of warning - artichokes are delicious, but they do cause flatulence, so this may not be the best dish to impress the girl/ boyfriend's parents, at least not unless you know them quite well already!