2 large leeks -- sliced

50 g butter

1 small onion -- chopped

1200 ml vegetable stock salt and freshly ground black pepper 25 g flour

150 ml milk

142 ml single cream

1. Melt half the butter in a large saucepan, add the leeks and onion and cook gently for 5 minutes until tender.

2. Add vegetable stock and seasoning, bring to the boil, cover and simmer for 15-20 minutes.

3. Meanwhile, melt remaining butter in a saucepan, stir in flour and cook gently for 1 minute. Gradually add the milk and cream, bring to the boil, stirring until thickened.

4. Mix the sauce with the leek mixture and then puree in a blender or food processor until smooth. Return to the saucepan and reheat gently.