I just made this again, really like it!

Creamy Jerusalem Artichoke soup

Olive oil
6-8 Jerusalem Artichokes
1-2 potatoes
1 small onion
1 clove of garlic
vegetable or chicken stock
salt
pepper

Cut a small onion and a clove of garlic in smaller pieces and put it in a pot with a bit of oil.

Peel the Jerusalem Artichokes, cut them into pieces and also the potatoes and put them in the pot. Add about 1/2 liter of vegetable stock or chicken stock. Bring to a boil and let it simmer for about 25 min. covered with a lid. Stir now and again.

Let it cool off a bit and pour into a blender and whirl it around. Pour it back into the pot and add about 1 dl of milk and/or cream and heat it. Add some salt and pepper to taste.

In case you don't know them, here's a picture. They come in a more round version, too. Get the ones without too many "bumps on them, they're so much easier too peel.
http://www.bbc.co.uk/food/jerusalem_artichoke

There's a thread with other good soups, called "Recipes - Soup" And there's one for Crockpot's, too.