The beauty of blending any members of the artichoke family into a soup like this is the way you instantly get a creamy and rich texture, with only the smallest amount of butter. Globe artichokes can of course be used, but if you can get the Jerusalem variety, their own natural nuttiness blends wonderully with the spice mix topping
2 large leeks
4 medium sticks of celery
400g Jerusalem artichokes
1 litre light stock or water
a small bunch of parsley
For the spice mix
1 tsp coriander seeds
30g shelled walnuts
30g fresh ginger
4 tsp groundnut oil
Discard the outer leaves from the leeks then cut into thin rounds. Rinse under running water, and then add them with the butter to a heavy saucepan. Let the leeks cook in the butter over a low heat for a good 15 minutes or so till they break down with the pressure from the back of a spoon.
Finely slice and add the celery, then peel and chop the artichokes and stir them in, too. Cover the pot with a lid so the vegetables sweat and soften without colouring, then pour in the stock and bring to the boil. Turn the heat down to a simmer, partially covered with a lid, this will take about 25 minutes for the artichokes to become tender.
Grind the coriander seeds to a fine powder and then add the walnuts, mashing them briefly to a pulp. Peel the ginger and slice thinly, then cut into thin matchsticks. Heat the oil in a shallow pan and fry the ginger for about 30 seconds till it's golden and crisp. Toss in the crushed walnuts and coriander; let them sizzle briefly then tip onto kitchen paper.
Liquidise the soup in a blender, stir in the parsley and check the seasoning. The soup should be mild and slightly nutty tasting. Ladle into bowls and top with ginger and spice mix.