In a saucepan sauté the spring onions, celery and thyme in the butter for 2-3 minutes. Add the mushrooms and soften till the juices run. Season with salt and pepper. Pour over the milk, bring to a simmer and add the cockles and diced potato. Heat through and serve.
If you are making the posh dinner party version, make the soup as above and then ladle into four ovenproof soup bowls. Mois