Butterbean and Mushroom Chowder

1 cup/l00g/4oz butter beans soaked overnight in cold water
1 tsp/5ml olive oil
2 onions, chopped
2 stalks celery, sliced
8oz/225g potatoes, peeled and diced
4oz/100g button mushrooms, sliced
1/2 cup/50g/2oz sweetcorn kernels
1 ? cups/300ml/ ? pt skimmed milk
Salt and freshly ground black pepper
2 tbsp/30ml chopped parsley
Serves 4-6
Drain the beans and place in a large saucepan covered with fresh water. Boil fast for 10 minutes, then simmer for a further 35- 40 minutes, or until soft.
Drain the beans and reserve 2 cups/ 450ml/ ? pt of the stock.
Heat the oil in a large saucepan and gently fry the onion. Add the celery and potato and cook for 2-3 minutes, stirring from time to time. Add the reserved stock and mushrooms, bring to the boil, cover and simmer for 10 minutes.