Jerusalem artichoke soup.

Hugh Fearnley-Whittingstall: Knobbly needs | Life and style | The Guardian: "Cream of Jerusalem artichoke soup
Throw these humble ingredients into a pot and the resulting soup is really very classy.
Especially when served with the pesto (see following recipe).
Serves six.
50g unsalted butter
1kg Jerusalem artichokes, peeled and cubed
350g leeks, washed and finely sliced
100g potato, peeled and cubed
1 medium onion, diced
2 garlic cloves, minced
1.6 litres chicken or vegetable stock
100ml double cream
Salt and pepper
Rapeseed oil, to finish (optional)

"In large, heavy-based saucepan, melt the butter over a low heat, then gently sweat all the vegetables until soft - about 20 minutes.
Add the stock, bring to a boil, then lower the heat and simmer, partially covered, for 20 to 30 minutes, until the artichokes can be easily mashed against the side of the pan with the back of a wooden spoon.
Leave to cool slightly.
Liquidise the soup until smooth (you may need to do this in batches), then return to the pot.
Warm over a medium heat, add the cream and season generously.
Serve in warmed bowls, topped with a spoonful of chestnut and parsley pesto (see following recipe), and finish with a swirl of rapeseed oil."
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