Watercress soup

• 2 bunches watercress
• 1 medium-sized onion
• 1 oz (

Pick off the leafy tops from the watercress and set aside a small handful for the garnish. Peel and finely chop the onion. Melt the butter in a large saucepan over low heat, add the onion and fry gently for 5 minutes to soften but not brown. Meanwhile, peel and cut the potatoes in even-sized chunks. Pour the stock into the pan, add the bay leaf and season with salt and pepper. Bring to the boil