Jerusalem artichoke soup

• 1 onion, sliced
• 50g/2oz butter
• 700g/1 1⁄2lb Jerusalem artichokes, peeled and sliced
• 600ml/1pt milk salt and ground white pepper

1. In a heavy saucepan over a low heat, gently sweat the onion in the butter until soft and translucent.
2. Add the artichokes to the onion. Cook, covered, for 10 minutes, stirring a few times.
3. Add 600ml/1pint water and the milk. Season with salt and pepper to taste, and simmer slowly – do not boil or the milk may curdle.
4. Purée the soup using a blender or food processor. Taste and add more seasoning if needed. Reheat gently and serve.