Legend has it that it was watercress that enabled St Brendan to live to the ripe old age of 180. In Birr Castle in Co Offaly, Lord and Lady Rosse still serve soup of watercress gathered from around St Brendan’s well, just below the castle walls.
12ozs (45g) butter
5ozs (140g) peeled and chopped potatoes
4ozs (110g) peeled and chopped onion
Salt and freshly ground pepper
1 pint (600ml) water or home-made chicken stock or vegetable stock
1 pint (600ml) creamy milk
8ozs (225g) chopped watercress (remove the coarse stalks first)
Melt the butter in heavy bottomed saucepan. When it foams, add the potatoes and onions and toss them until well coated. Sprinkle with salt and freshly ground pepper. Cover and sweat on a gentle heat for 10 minutes.
Meanwhile, prepare the watercress. When the vegetables are almost soft but not coloured add the stock and milk, bring to the boil and cook until the potatoes and onions are fully cooked. Add the watercress and boil with the lid off for 4-5 minutes approx. until the watercress is cooked. Do not overcook or the soup will lose its fresh green colour.
Puree the soup in a liquidiser or food processor. Taste and correct seasoning.