Jerusalem Artichoke and Celeriac Soup

700g Jerusalem artichokes, peeled and diced
500g celeriac, peeled and diced
30g unsalted butter
1 onion, chopped
1.4 litres fresh vegetable stock
50ml single cream
2 tablespoons chopped chives
Serves: 4

1 Put the diced Jerusalem artichokes and celeriac in a bowl of cold, salted water.
2 Melt the butter in a large saucepan and cook the onion gently until soft and translucent.
3 Drain the artichokes and celeriac and add to the onion. Season and cook for 5 minutes, stirring frequently, until the vegetables have softened slightly.
4 Add the stock and bring to the boil. Then cover and simmer for 20−25 minutes until the vegetables are tender.
5 Transfer to a blender − in batches if necessary − and blend until completely smooth.
6 Return to the pan, adding the single cream, and reheat gently.
7 Serve with a little extra cream, chives and croutons.

Recipe from Waitrose Food