Instructions

1. Finely chop the onion, garlic and celery.
2. Heat 1 tbsp. olive oil in a saucepan and gently sauté the chopped vegetables. Meanwhile, peel and dice the potato.
3. Add the diced potatoes, stir for a minute, then add the stock. Bring to the boil and cook for 10-15 minutes until the potatoes are tender.
4. Add the peas and cook for 5 more minutes.
5. Turn off the heat and add the watercress.
6. Transfer the soup to a liquidiser, or, using a stick blender, pulse until you get a smooth, silky soup.
7. Serve with a squeeze of lemon juice.